Increasing Spawn Rates in a Specific Custom Biome

I've been having issues in a custom biome in a custom dimension where very few mobs are spawning. All the mobs allowed to spawn there are custom and there are around 6 of them, all with similar spawn weights and groups. The Issue became more prevalent with the more mobs I added, and now the biome is very desolate. All of the mobs are ambient to allow them in spawn in light, as there is a lot of fire in the biome. Only around 10 to 15 mobs will spawn at once and I want the spawn rate to be much greater. Any response is greatly appreciated.