For example, If I were to upload this image as an avatar:
It would be resized (very roughly, I don't know the exact dimensions) to this by XenForo:
I would prefer the aspect ratio to be kept, and for the avatar to come out something like this:
I believe the ImageMagick options I'd use would be something like this, if it makes my point easier to understand:
convert avatar.png -resize x125
Thanks for looking!