Perhaps my experiences have been luckier than most. In a 54g corner I have had a pr of black ocellaris and a pr of reg ocellaris together for the past 3 yrs with no problems,
In a 72g bowfront I have had a pr of ocellaris and a pr of pink skunks for the past 2yrs.
And in a 90g I have a pr with a female black ocellaris a male reg ocellaris and a pr of pink skunk clowns for the past 3 yrs.
Every time I have tried multiple prs of clowns it has worked, I just stayed with the smaller species, added them as close together as possible, tried to get them as small as possible, and if added at different times, try to add the new ones at the opposite side of the tank close to lights out.