Lean top is a possibility but I still think this is mechanical. I have a B7 too (love that thing) and it runs great with a cold plug but if you run 20% you can easily get away with a warmer plug (McCoy MC-59 or something like that) and get better idle and resistance to tuning errors. A cold plug becomes necessary with 30% fuel so that you don't get detonation at higher engine speeds.
What kind of clutch setup are you using?
230 is about right for these. I go more like 250 but don't tune anything until it is fully warmed up. Collaris take FOREVER to warm up, much longer than any other engine I've seen and then they like to run warm. Don't get hung up on trying to get down to 210 like other guys.