It just depends. If you don't mind your corals going to war then you can cram them. My tank is literaly covered in different zoas shrooms
and polyps. Then the occasional trumpet Frogspawn colt and torch corals. My zoas and shrooms
have been in a territory war for a couple of weeks now. The shrooms
are managing to cover the zoas but the zoas spread rapidly and are trying to grow around them. You just have to be careful and watchful with some. I have a trumpet which got close to a green mushroom and the mushroom surprisingly almost killed three heads on it. I moved it and it's getting better. I also had a Frogspawn fall over on a red mushroom almost killing the mushroom but the shroom bounced back and is doing better. With me, I don't mind if my "weed" corals go to war, they'll spread quickly and no matter which one wins it'll look beautiful covering my tank. But with my stonies, I move them when needed. Look at my 90 gallon pics. I plan on posting a YouTube video soon just so you can see how close everything is.