sorry, i was looking at the wrong gallery
this goes back to my original answer in this thread.
image size settings are taken from this line in the
$gallery = get_gallery(get_mediarss_url('gallery=' . $pg_id . '&thumb=62c&full=782p'));
this is using a cropped image for the thumbnail:
you could set it to use a proportional image instead:
but that will not give uniform sizes to the thumbnail. in order to have the thumbnails use uniform sizes, a roped image must be used.