I'm trying to get zombies and skeletons and their spawn rates jacked up to two-three times the normal, especially since my modpack (1.12.2) for some reason is making them spawn significantly less than normal. However, it's not working.

This is what I tried:
[
{
"mob": "Zombie",
"weight": 200,
"groupcountmin": 3,
"groupcountmax": 10
},
{
"mob": "skeleton",
"weight": 120,
"groupcountmin": 1,
"groupcountmax": 5
}
]