Have you tried making the avatar slightly smaller than the maximum dimensions? Also try putting a border around the transparent avatar in the largest allowable dimension but make it the colour of the forum background (C9C9C9).
"Fight The Power, Protect The Downtrodden. Blah Blah, Woof Woof!"
Thanks to | pre)Ghost | KANA Lock | BtheVampireSlayer | ABrown | Destiny | Abk | for the Katrina Law sigs.