Why does my avatar keep shrinking in size?

I keep trying to put larger images (like what Ruta and Munroe have), but the fucking forums keep constricting the size on it.

What the fuck? Help please.

Upload your avatar onto on off-site location (such as imageshack or photobucket) and put the URL into the avatar field where it says "Link to an off-site avatar". This allows you to bypass the filesize limit, and I think the dimension limit (150x200). It also lets you have your avatar as a transparency (uploading transparencies with the default settings causes them to have white backgrounds).

Thanks, now it's the size I want it