Rule of thumb, you can mix a dwarf and a regular but not two of the same. Yes tanks size comes into play. Its not so much the large angels its the dwarfs they are more aggressive than the large ones because of the habitate they like, they tend to hang around the live rock more. Dwarfs will pic on the larger angels but they can take it. I had a half black angel in with a big koran angel they were fine together when i added a bicolor angel stuff went down hill from there. had to move the bi color out into a tank by himself. But in a big tank like that you shouldnt have any problems. Good luck