I have two in my 225g that have literally been together for 5 years. They were in my LFS show tank for 3 years, and I have had them in my possession for 2 years. To my knowledge, they have never been around any other or a large group of other chromis. Just the two of them in every tank they've been in (except at the distributor)...
I say all of this to say that two chromis in a 225g will still bicker over hierarchy every now and then. Mine do the kissing thing all of the time, but I have very rarely seen any outright aggression or fighting between the two though it does happen on occasion. The reason I equate this with fighting is that the kissing will happen without a fight most of the time. But when they do swipe at eachother, it is both lead by, and followed up with aggressive "kissing" so to speak. So, they kiss without fighting, but never fight without kissing...
It's a little weird because they follow eachother around feeding together, sleeping together, hiding together, etc...
Also: I've never considered adding any additional chromis to my tank. My tank could probably support a few more, but these seem happy enough with just the two of them. I wouldn't want to risk adding chaos into my tank by adding more chromis. It may work, but it may not. They seem to be able to thrive under their current conditions, and haven't killed each other or even excessively bullied each other for 5 years at least. Don't want them to start now. LOL...