Hello everyone.
I'm making a map, and I want to have a Witch spawner to spawn Witch at specific coordinates. I want the spawn to be random, so I can't use the /summon command.
As Witch has spawn conditions that I don't want, I summon them riding Endermite, as they haven't.
To control spawns, I also spawn them from a Spawner Minecart, spawned by a Mob Spawner.
So I summoned the spawner with this command in a command block :
blockdata ~ ~1 ~ {MaxNearbyEntities:1s,RequiredPlayerRange:1600s,SpawnCount:1s,MaxSpawnDelay:1s,
id:"minecraft:mob_spawner",SpawnRange:2s,MinSpawnDelay:1s,SpawnPotentials:[{Entity:{
id:"minecraft:spawner_minecart",MaxNearbyEntities:80s,RequiredPlayerRange:1600s,SpawnCount:1s,
MaxSpawnDelay:30s,MinSpawnDelay:30s,Delay:20s,SpawnRange:20s,Pos:[397.5d,157d,474.5d],SpawnPotentials:[{
Entity:{id:"minecraft:endermite",Pos:[460.5d,171d,461.5d],Passenger:[{id:"minecraft:witch",
Pos:[460.5d,171d,461.5d]}]},Weight:1},{Entity:{id:"minecraft:endermite",Pos:[420.5d,171d,461.5d],
Passengers:[{id:"minecraft:witch",Pos:[420.5d,171d,461.5d]}]},Weight:1},{Entity:{id:"minecraft:endermite",
Pos:[440.5d,171d,481.5d],Passengers:[{id:"minecraft:witch",Pos:[440.5d,171d,481.5d]}]},Weight:1},{Entity:{
id:"minecraft:endermite",Pos:[440.5d,171d,441.5d],Passengers:[{id:"minecraft:witch",
Pos:[440.5d,171d,441.5d]}]},Weight:1}]},Weight:1}]}But it doesn't work : I don't see any mob spawning from the Spawner Minecart, as :
blockdata ~ ~1 ~ {MaxNearbyEntities:1s,RequiredPlayerRange:1600s,SpawnCount:1s,MaxSpawnDelay:1s,
id:"minecraft:mob_spawner",SpawnRange:2s,MinSpawnDelay:1s,SpawnPotentials:[{Entity:{
id:"minecraft:spawner_minecart",MaxNearbyEntities:80s,RequiredPlayerRange:1600s,SpawnCount:1s,
MaxSpawnDelay:30s,MinSpawnDelay:30s,Delay:20s,SpawnRange:20s,SpawnPotentials:[{Entity:{
id:"minecraft:endermite",Passenger:[{id:"minecraft:witch"}]},Weight:1},{Entity:{id:"minecraft:endermite",
Passengers:[{id:"minecraft:witch"}]},Weight:1},{Entity:{id:"minecraft:endermite",Passengers:[{
id:"minecraft:witch"}]},Weight:1},{Entity:{id:"minecraft:endermite",Passengers:[{id:"minecraft:witch"}]},
Weight:1}]},Weight:1}]}Is working, but is not what I want.
Does any one knows what is the problem ?

Also :
- I'm on Minecraft JE 1.12.2
- This method is working with Magma Cube, but I didn't use command, I use NBTExplorer, which doesn't work in this case too
- The problem seems really to be the position

Thanks for responding, and sorry for possible mistakes.