Try removing {vb:raw prepared.avatarsize} from the stuff you added to the memberinfo_block_ministats template. Edit:...actually I don't think that's going to do it, still working on it....
OK, you also need a plugin. Go to "Add New Plugin" under "Plugin & Products".
Leave the product dropdown at "vbulletin" and select "member_profileblock_fetch_unwrapped" from the Hook Location dropdown menu.
Next, enter a title, maybe something like "full size avatar in profile". Then paste this code in the large text area:
Code:
if (!empty($prepared['avatarurl']))
$prepared['avatarurl'] = str_replace('&type=thumb', '', $prepared['avatarurl']);
Now select the Yes radio button next to "Plugin is Active", and press Save.
Hopefully that will do it.