They all do grow at different rates that's very true. Have you ever tried offering him a second f/t mouse during his weekly feed? Does he show any indication of continuing to actively hunt for a long while after he eats his mouse? Does he seem very hungry days before he's due to eat again (not just 24 hours or so before but days and days before)? How does the biggest part of the mouse (usually it's hips/butt) compare to his largest empty girth?