I think you want a shape that will be stalled quickly and not provide any lift to cause your planing. Your broad-head is the equivalent of a delta wing, the worst shape for you application. The Delta doesn't stall, and makes it's lift by vortex generated lift. It would seam to me that a highly swept thin wing would stall very quickly. If I were to try to make this non-planing head it would be swept back 60*, maybe 1/4" chord on the "wing", and I would airfoil it with a diamond shaped airfoil.