How far away does a not related scoly need to be from each other

[Nordy]

Hello, I will have 2 Croc island Scolys that are near each other and I’ll be receiving this Scoly today. The 2 Croc island Scolys would be about 4 inches above this new one if I place it where I’m thinking. Is this too close?

 

[encrustingacro]

From what I know, neither regular Scolys (Homophyllia australis) and croc islands (cf Micromussa pacifica) are agressive.