Turns out I still had my test forum from before the 2.0 update on NF rolled out. I'm assuming things didn't change too much since, so you can probably go to message_macros and find this line: <xf:avatar user="$user" size="m" defaultname="{$fallbackName}" itemprop="image" /> Change the size from M to whatever you want (I'd go with L, lowercase). You're gonna wanna use CSS to then shrink it down to 175px tops (since that appears to be the size you're working with in your postbit), which you can do pretty easily by targeting the element in extra.less or probably just by adjusting style properties on a per skin basis. I tested it and it works.