Mmmm...
I have done a LITTLE bit of research and much depends on what family of fungus we are talking of.

They are quite diversified and it seems like more than half of them are still unknown to us today.
I do know that mushrooms are really diversified and tend to adapt.

I also went searching for maps where you had fungus biome and well, me found nothing on the internet. I must admit I never was good to search what I need on google so maybe someone could help us all by posting a link or an icone for mushroom biome in cartography?

One thing that could be interesting with the mushrooms is that some of them tend to live with other types of plants. Maybe we need to look into what possible ally or victime to add in a fungus biome. As ally, moss on rocks would allow some mushrooms to grow near, but they probably won't be as big as we want. Another possibility would be to have a dying forest, which would be a transition from a wooded area to a mushroom paradise. But once the wood is consumed and desintegrated, on what will mushroom live? Maybe a mushroom biome could exist on the basis of rotation.
1-Mushroom growing from dead trees or trunks.
2-When wood is scarce, those first mushrooms die and all the humidity and moisture now serves to grow ANOTHER kind of mushroom, here sprouting from the ground.
3-After a while, the soil gets dry and and loose some nutrients in some dry season, which cause some kind of mushrooms to go in sleeping, letting therefore the earth rest for a while.