Increasing the height of the Nether using custom JSON world generator files does not increase the height at which groundcover such as soulsand or basalt or nylium generate.

World generator json.

{
"bonus_chest": false,
"dimensions": {
"minecraft:overworld": {
"generator": {
"biome_source":

{ "seed": 1, "large_biomes": false, "type": "minecraft:vanilla_layered" }

,
"seed": 1,
"settings": {
"bedrock_roof_position": -10,
"bedrock_floor_position": 0,
"sea_level": 4,
"disable_mob_generation": false,
"default_block": {
"Name": "minecraft:stone",
"Properties": {}
},
"default_fluid": {
"Name": "minecraft:lava",
"Properties":

{ "level": "0" }

},
"noise": {
"top_slide":

{ "target": -35, "size": 32, "offset": 0 }

,
"bottom_slide":

{ "target": -3, "size": 6, "offset": 1 }

,
"sampling":

{ "xz_scale": 1, "xz_factor": 150, "y_scale": 1, "y_factor": 50 }

,
"size_vertical": 2,
"size_horizontal": 1,
"height": 256,
"density_factor": 0.1,
"density_offset": -0.05,
"random_density_offset": true,
"simplex_surface_noise": true,
"island_noise_override": false,
"amplified": false
},
"structures": {
"stronghold":

{ "distance": 32, "count": 128, "spread": 3 }

,
"structures": {
"minecraft:village":

{ "spacing": 32, "separation": 8, "salt": 10387312 }

,
"minecraft:desert_pyramid":

{ "spacing": 32, "separation": 8, "salt": 14357617 }

,
"minecraft:igloo":

{ "spacing": 32, "separation": 8, "salt": 14357618 }

,
"minecraft:jungle_pyramid":

{ "spacing": 32, "separation": 8, "salt": 14357619 }

,
"minecraft:swamp_hut":

{ "spacing": 32, "separation": 8, "salt": 14357620 }

,
"minecraft:pillager_outpost":

{ "spacing": 32, "separation": 8, "salt": 165745296 }

,
"minecraft:stronghold":

{ "spacing": 1, "separation": 0, "salt": 0 }

,
"minecraft:monument":

{ "spacing": 32, "separation": 5, "salt": 10387313 }

,
"minecraft:endcity":

{ "spacing": 20, "separation": 11, "salt": 10387313 }

,
"minecraft:mansion":

{ "spacing": 80, "separation": 20, "salt": 10387319 }

,
"minecraft:buried_treasure":

{ "spacing": 1, "separation": 0, "salt": 0 }

,
"minecraft:mineshaft":

{ "spacing": 1, "separation": 0, "salt": 0 }

,
"minecraft:ruined_portal":

{ "spacing": 40, "separation": 15, "salt": 34222645 }

,
"minecraft:shipwreck":

{ "spacing": 24, "separation": 4, "salt": 165745295 }

,
"minecraft:ocean_ruin":

{ "spacing": 20, "separation": 8, "salt": 14357621 }

,
"minecraft:bastion_remnant":

{ "spacing": 27, "separation": 4, "salt": 30084232 }

,
"minecraft:fortress":

{ "spacing": 27, "separation": 4, "salt": 30084232 }

,
"minecraft:nether_fossil":

{ "spacing": 2, "separation": 1, "salt": 14357921 }

}
}
},
"type": "minecraft:noise"
},
"type":

{ "name": "minecraft:overworld", "ultrawarm": false, "natural": true, "shrunk": false, "piglin_safe": false, "respawn_anchor_works": false, "bed_works": true, "has_raids": true, "has_skylight": true, "has_ceiling": false, "ambient_light": 0.0, "logical_height": 256, "infiniburn": "minecraft:infiniburn_overworld" }

},
"minecraft:the_nether": {
"generator": {
"biome_source": {
"seed": 1,
"type": "minecraft:multi_noise",
"biomes": [
{
"biome": "minecraft:basalt_deltas",
"parameters":

{ "temperature": -0.5, "humidity": 0, "altitude": 0, "weirdness": 0, "offset": 0.175 }

},
{
"biome": "minecraft:crimson_forest",
"parameters":

{ "temperature": 0.4, "humidity": 0, "altitude": 0, "weirdness": 0, "offset": 0 }

},
{
"biome": "minecraft:nether_wastes",
"parameters":

{ "temperature": 0, "humidity": 0, "altitude": 0, "weirdness": 0, "offset": 0 }

},
{
"biome": "minecraft:soul_sand_valley",
"parameters":

{ "temperature": 0, "humidity": -0.5, "altitude": 0, "weirdness": 0, "offset": 0 }

},
{
"biome": "minecraft:warped_forest",
"parameters":

{ "temperature": 0, "humidity": 0.5, "altitude": 0, "weirdness": 0, "offset": 0.375 }

}
]
},
"seed": 1,
"settings": {
"bedrock_roof_position": -10,
"bedrock_floor_position": -10,
"sea_level": 0,
"disable_mob_generation": false,
"default_block": {
"Name": "minecraft:netherrack",
"Properties": {}
},
"default_fluid": {
"Name": "minecraft:lava",
"Properties":

{ "level": "0" }

},
"noise": {
"top_slide":

{ "target": -150, "size": 20, "offset": 0 }

,
"bottom_slide":

{ "target": -10, "size": 8, "offset": -1 }

,
"sampling":

{ "xz_scale": 1, "xz_factor": 80, "y_scale": 3, "y_factor": 60 }

,
"size_vertical": 2,
"size_horizontal": 1,
"height": 256,
"density_factor": 0,
"density_offset": 0.02,
"random_density_offset": true,
"simplex_surface_noise": false,
"island_noise_override": false,
"amplified": false
},
"structures": {
"structures": {
"minecraft:village":

{ "spacing": 32, "separation": 8, "salt": 10387312 }

,
"minecraft:desert_pyramid":

{ "spacing": 32, "separation": 8, "salt": 14357617 }

,
"minecraft:igloo":

{ "spacing": 32, "separation": 8, "salt": 14357618 }

,
"minecraft:jungle_pyramid":

{ "spacing": 32, "separation": 8, "salt": 14357619 }

,
"minecraft:swamp_hut":

{ "spacing": 32, "separation": 8, "salt": 14357620 }

,
"minecraft:pillager_outpost":

{ "spacing": 32, "separation": 8, "salt": 165745296 }

,
"minecraft:stronghold":

{ "spacing": 1, "separation": 0, "salt": 0 }

,
"minecraft:monument":

{ "spacing": 32, "separation": 5, "salt": 10387313 }

,
"minecraft:endcity":

{ "spacing": 20, "separation": 11, "salt": 10387313 }

,
"minecraft:mansion":

{ "spacing": 80, "separation": 20, "salt": 10387319 }

,
"minecraft:buried_treasure":

{ "spacing": 1, "separation": 0, "salt": 0 }

,
"minecraft:mineshaft":

{ "spacing": 1, "separation": 0, "salt": 0 }

,
"minecraft:ruined_portal":

{ "spacing": 25, "separation": 10, "salt": 34222645 }

,
"minecraft:shipwreck":

{ "spacing": 24, "separation": 4, "salt": 165745295 }

,
"minecraft:ocean_ruin":

{ "spacing": 20, "separation": 8, "salt": 14357621 }

,
"minecraft:bastion_remnant":

{ "spacing": 27, "separation": 4, "salt": 30084232 }

,
"minecraft:fortress":

{ "spacing": 27, "separation": 4, "salt": 30084232 }

,
"minecraft:nether_fossil":

{ "spacing": 2, "separation": 1, "salt": 14357921 }

}
}
},
"type": "minecraft:noise"
},
"type":

{ "name": "minecraft:the_nether", "ultrawarm": true, "natural": false, "shrunk": true, "piglin_safe": true, "respawn_anchor_works": true, "bed_works": false, "has_raids": false, "has_skylight": false, "has_ceiling": false, "fixed_time": 18000, "ambient_light": 0.1, "logical_height": 256, "infiniburn": "minecraft:infiniburn_overworld" }

},
"minecraft:the_end": {
"generator": {
"biome_source":

{ "seed": 1, "type": "minecraft:the_end" }

,
"seed": 1,
"settings": {
"bedrock_roof_position": -10,
"bedrock_floor_position": -10,
"sea_level": 0,
"disable_mob_generation": true,
"default_block": {
"Name": "minecraft:end_stone",
"Properties": {}
},
"default_fluid": {
"Name": "minecraft:air",
"Properties":

{ "level": "0" }

},
"noise": {
"top_slide":

{ "target": -3000, "size": 64, "offset": -46 }

,
"bottom_slide":

{ "target": -30, "size": 7, "offset": 1 }

,
"sampling":

{ "xz_scale": 2, "xz_factor": 80, "y_scale": 1, "y_factor": 160 }

,
"size_vertical": 1,
"size_horizontal": 2,
"height": 128,
"density_factor": 0,
"density_offset": 0,
"random_density_offset": false,
"simplex_surface_noise": true,
"island_noise_override": true,
"amplified": false
},
"structures": {
"structures": {
"minecraft:village":

{ "spacing": 32, "separation": 8, "salt": 10387312 }

,
"minecraft:desert_pyramid":

{ "spacing": 32, "separation": 8, "salt": 14357617 }

,
"minecraft:igloo":

{ "spacing": 32, "separation": 8, "salt": 14357618 }

,
"minecraft:jungle_pyramid":

{ "spacing": 32, "separation": 8, "salt": 14357619 }

,
"minecraft:swamp_hut":

{ "spacing": 32, "separation": 8, "salt": 14357620 }

,
"minecraft:pillager_outpost":

{ "spacing": 32, "separation": 8, "salt": 165745296 }

,
"minecraft:stronghold":

{ "spacing": 1, "separation": 0, "salt": 0 }

,
"minecraft:monument":

{ "spacing": 32, "separation": 5, "salt": 10387313 }

,
"minecraft:endcity":

{ "spacing": 20, "separation": 11, "salt": 10387313 }

,
"minecraft:mansion":

{ "spacing": 80, "separation": 20, "salt": 10387319 }

,
"minecraft:buried_treasure":

{ "spacing": 1, "separation": 0, "salt": 0 }

,
"minecraft:mineshaft":

{ "spacing": 1, "separation": 0, "salt": 0 }

,
"minecraft:ruined_portal":

{ "spacing": 40, "separation": 15, "salt": 34222645 }

,
"minecraft:shipwreck":

{ "spacing": 24, "separation": 4, "salt": 165745295 }

,
"minecraft:ocean_ruin":

{ "spacing": 20, "separation": 8, "salt": 14357621 }

,
"minecraft:bastion_remnant":

{ "spacing": 27, "separation": 4, "salt": 30084232 }

,
"minecraft:fortress":

{ "spacing": 27, "separation": 4, "salt": 30084232 }

,
"minecraft:nether_fossil":

{ "spacing": 2, "separation": 1, "salt": 14357921 }

}
}
},
"type": "minecraft:noise"
},
"type": "minecraft:the_end"
}
},
"seed": 1,
"generate_features": true
}