Someone needs to send you some deer hide. I bet the bullets will perform better than the carpet/plywood.
I appreciate what you're doing, but I feel it's more of a torture test than a simulation. An easily expanding bullet will never do well in the test. Other than a bullet like a Bloodline that will blow off the petals with any resistance, and is just like a hard cast bullet after that. Bullets that are known game killers could look bad in the test.