After much searching I think i've finally pinpointed the cause of the picture alignment (as described earlier)
The display pictures in the conversation window have small amounts of padding around them.
I'm unable to ascertain whether this padding is in the UI files, or in the picture files themselves, as any chance that I make seems to have no effect
The pictures themselves (4400_var, 4401_var, etc) DO have blank space around them corresponding to the gap that's left when I try to add a picture sitting ontop of the display picture.
So I tried adding a new resource without that space around it and replacing it in the UI files, but it made no difference (and I tried setting the 'online' one to be there for every single status, but it didn't change)
I also notice that there's padding in the style file against idUserTileContainer, which I tried setting all of them to 0, but again nothing changed
So it seems like I'm close to being able to solve the problem (and therefore release my skin), but I just can't seem to figure it out