Avatars may not work in sub-networks.
In order to ensure consistancy a location must be hard set.
Either in a MU plugin (Such as this one)
or in WP-Config like this
//SITEWIDE AVATAR DIR & URL
define( 'BP_AVATAR_UPLOAD_PATH', '/path/to/public/avatars' );
define( 'BP_AVATAR_URL', 'http://website.com/avatars' );
I hope this helps someone, if so drop by my person site and say "hi" sometime.