When I did my import in October, my avatars were all enlarged as well. It was because they all imported with width=0 and height=0. I don't know if that's the case with yours or not, but Rick had me run this to replace all the 0's with 64's. If that is the case with your import, you'd need to change 64 with whatever avatar sizes you're using (if they're all the same)...
Code
update ubbt_USER_PROFILE set USER_AVATAR_WIDTH='64',USER_AVATAR_HEIGHT='64' where USER_AVATAR_WIDTH='0' and USER_AVATAR_HEIGHT='0'

[*BUG* Rick, when I don't put spaces before and after the code, when enclosed in CODE tags, I get nothing when I Preview Post -- and apparently also in the post itself. It does show up if I add a CR after the CODE tag]

Code
update ubbt_USER_PROFILE set USER_AVATAR_WIDTH='64',USER_AVATAR_HEIGHT='64' where USER_AVATAR_WIDTH='0' and USER_AVATAR_HEIGHT='0'



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