usually same species of corals can touch each other without much conflict. rhodactics can touch other rhodactics, yumas to yumas, euphyllias to euphyllias, cataphyllia to cataphyllia... etc etc etc. the only problem is, the parts that are touching each other may limit the growth due to space competition or like vt snowman mentioned, hading of the bigger and more dominant one. hope this helps u
This can help u maximise space in ur tank also. all ur zoos for example, can be put near each other to make a niec bunch all euphyllias(hammer, torch, frogspawn) can be placed near each other without much problem. when they grow too big, just shift around a little