I would tend to agree mice are not really a great meal for Royals they are simply too small. Ideally I would be feeding a male that size 1000gm around 100gm a week (small rat) until he hits the 1400-1600gm or so and then reduce that 10% weight to hold around the 5-7% so basically 70-110gm prey every 7 days. This allows them to attain full growth and then they go on a maintenance diet, to hold them.

Most of my adult males are 1600-2000 gm.