there's alot of good info here but I am surprised you havent gotten in contact with thomas at www.vqwarbirds.com since he is a distributor he might have some insite into this plane and its quirks.
there's several dist. of VQ warbirds but thomas is very helpfull to those who ask
rather than making guesses as to the problem there might be some simple fix to help with the roll problem rather than the trial and error method.
from what I have read as well as richard lee who is a real expert in these arfs http://www.warbirdobsession.com/ he is a moderator on RCU and has alot of insite in the VQ line of planes as well.
lastly you didnt post this in the warbirds section being a warbird,there is alot of info there on these arfs as well.