One thing I suspect, after seeing quite a few on the ground, is that smaller-diameter bullets of the "petal" type (whether the Combined Technology Fail Safe, Barnes X, Nosler E-Tip or Hornady GMX) penetrate the off-side hide somewhat better, because the mushroom isn't nearly as as large. As an example, on my last nilgai hunt a couple years ago saw the .30 caliber 150 Hornady GMX completely penetrate one big bull broadside, leaving a nice blood trail--which really wasn't needed. Also saw the same thing with more than one .270 Fail Safe during a hunt a number years ago, when a dozen bulls were taken with .270 WSM's.

“Montana seems to me to be what a small boy would think Texas is like from hearing Texans.”
John Steinbeck