This is why I bought a RD straightening tool - it's the first thing to check to make sure all your subsequent adjustments aren't on the piss because something got bent. Reminds me I need to check mine again after I dropped the bike.
Interesting the university bike workshop has one so I might give it a check anyway but I figured the fact that I had just replaced the derailleur hanger itself would mean that it was likely straight.
So you RD might've been adjusted for a slightly bent one or maybe there's a slight difference in position with the new one bolted down. I know my Tripster hanger has scope for some movement so you need to be careful when bolting it down (and I need to stop destroying RDs)
This is why I bought a RD straightening tool - it's the first thing to check to make sure all your subsequent adjustments aren't on the piss because something got bent. Reminds me I need to check mine again after I dropped the bike.