How to stop flying entities from floating in the air? plus one more question.

Hi! I already know that this topic has already been discussed, tho it didn't work for me, and I still don't know how to fix the problem. Can anyone tell me how to stop flying entities from floating in the air? 

I also have another question. How do you make something spawning in a biome in a specific location? I don't know if this is possible because when creating a new world with the mod, it will create a new map, with a new Minecraft world with the biome revamped.