Biome generation

I've posted on the discord before that I wanted to make a world generation datapack that would generate a big ocean with some islands. I have managed to do this but, right now, the mushroom fields biome is spawning way too much. How can I make the mushroom fields biome to be rarer? To achieve the islands I've changed the continentalness.json to this: { "amplitudes": [ 0.75, 0.75, 0.75, 0.75, 0.75, 0.75, 0.75, 0.75, 0.75 ], "firstOctave": -9 }