when he eats you should be able to look and see a slight bulge in his stomach. if he looks the same before eating as he does after then i would surely just try another mouse for now. you can try a weaned rat instead of 2 large mice but some dont wanna switch to rats. as for the jumbo comment if you have an 07 eating jumbos your not feeding jumbo rats. ive never seen a reason to give a ball more than a medium rat and those are large females in the 4000 gram range or better.

almost every place size rodents differently i typically use http://www.rodentpro.com/ for sizing