to increase would require more info
but with the info provided, I would suggest switching as many of your mice eating snakes over to rat pups if you can...
down sizing your mouse breeding and increasing your rat breeding.
I would increase the colony sizes in the concrete mixing tubs and personally...in any situation where large rats are needed...I would do away with the birthing rack...
Turn your birthing rack into a grow out rack...
purpose of a birthing rack is to allow mothers time to rest...in a production set up resting is bad. The more they produce continuosly, the quicker they will grow and the fatter they will get at a younger age...(these are your larges you will eventually be feeding)
Does each snake only eat one rat at the given size? How often do you feed them? how many mice do you have in a colony?