I have done the same test you did but come up with different results. The test is flawed right from the get go because foam targets are very poor mediums to test penitration on because of the way they stop an arrow.

Also the differences in your arrow weights were not very large either. Both were relitively heavy arrows and fairly close in weight.

I have done this test repeatedly with extremes of 100 grns or more and the heavier arrows always hit the the target harder, which would mean more penitration on live game with a blade type head.

Paul