Bob.B,
This is my opinion and only an opinion, no science to back it up. Not only should the bevel match the helical of the fletch, but the rate of rotation should match as well. The bevel on a Grizzly, for example, is designed to make it rotate through the animal at a farely slow rate; in my experience about 1/4 revolution from one side of a deer to the other. If you have a lot of fletch with a pretty a good helical inducing a farely high rate of spin on the arrow, then quite a bit of energy is used up at the moment of impact, inducing torque into the arrow shaft, thus reducing penetration. I personally shoot 190 gr Grizzly El Grandes with three 4 inch low profile feathers set with very little helical. My arrows corkscrew through the animal with very little resistance rather than drilling through.
If this sounds like hogwash then experiment yourself with different angles on your helical. A fast spinning BH will cause tremendous blunt force trauma. My set up virtually slips through with no blunt force trauma whatsoever.
Brett