I'm making some blocks with a vertical slab-like collision box, as well as some quarter half slabs I guess you could say (vertical trapdoor cut in half from bottom to top making it half a block on x, a full 16 on Y and 1 pixel on z). I used this code:

"minecraft:collision_box":

{                 "origin": [4, 0, 6.5],                 "size": [8, 16, 1] }

 

but got this error:

[Blocks][error]-block_definitions | C:/Users/goose/AppData/Local/Packages/Microsoft.MinecraftUWP_8wekyb3d8bbwe/LocalState/games/com.mojang/development_behavior_packs/BP Name | blocks/entity_name.json | namespace:entity | components | minecraft:collision_box: min can't be below (-8, 0, -8) and max can't be more than (8, 16, 8)

I get that 4 + 8 > 8 maybe that is the issue but in blockbench it is clearly within the 16x16x16 space of a regular block.

 

Update:
I have made an iron bar like block and the collision box is not where it is shown to be in blockbench. I'll continue testing to find out if blockbench is just displaying the collision box incorrectly or whether this is an issue with the game. Attached there are two more images: one of the iron bar in blockbench where the geometry and collision box match. One in game where the geometry is on my left (the correct spot) but the collision box is on my right.