Just a head's up, there might be something in this:
https://xenresources.com/threads/bigavatar-problem.96/#post-801
That particular post is very old and certainly there have been a number of changes in the Gallery which may make it no longer work. I'm assuming that's a slightly modified version of the Big and Tall avatar CSS, I'm not entirely sure. Certainly the only line there specific to the Gallery seems to be this:
Code:
.xengallery_view .messageUserInfo a.avatar img
That line would now probably be:
Code:
.mediaComments .messageUserInfo a.avatar img