Can you post a pic of the snake next to both sizes of feeders?
An adult male should be okay with just a small rat every 7 to 10 days, they don't need a ton of food. However, when I think small rat, I'm thinking a 4 to 6 week old rat that's just big enough to be separated from the momma rat. That may not be how rodent pro packages their smalls.
-Jen