Corns can take prey that is 1-1.5 times their body diameter, and often should. But what they should take isn't always what they will.

I've learned over time to combine plans like that with personal knowledge. For instance, my Anery corn girl is getting big, over 100g now, but I still feed her large hopper mice every 5 days because every time I've tried something a bit bigger she regurges it.
One of my BPs are similar in that she refuses to even go near anything larger than a large adult mouse and will only ever take one prey item. Because of this stubborness, she is rather small for her age...but I would rather have her small than on a hunger strike again.

Try offering prey that is up to 1.5 times again the snake diameter for corns and up to the same diameter for BPs, and keep in mind the weight ratios, but also listen to the snakes themselves and give them what they'll take.