What happened over time, and test, is we ran out of the shelving we started with. The shelving was given by the lady instead of her tossing it. When it was gone, it was replaced by some thicker plywood found out in the garden shed. Right away, it seemed the thicker stuff, skewed the results, and another test or two, revealed it did indeed. The thicker plywood was re-sawn, and now is about the same thickness as the original shelving.
It may be some material will have to be purchased, but for now the goal is to use up what is laying around here. Hopefully, hunting season will start, before we run out of scrap plywood.