Reproduction steps:

1. use 

   /give @p minecraft:creeper_spawn_egg{EntityTag:{CustomName:' {"text":"test"}
   ',CustomNameVisible:1b,NoAI:1b}}

1. and 

   /give @p minecraft:creeper_spawn_egg{EntityTag:{CustomName:' {"text":"deadmau5"}',CustomNameVisible:1b,NoAI:1b}}

1. place both spawn eggs
2. result: you can see that the nametag height is different when the entity is named "deadmau5".