Then, if I read y'all right, if you observe the sequence of the pattern changes, you should be able to roughtly predict the slower and faster sweet-spots. Which is to say you should know by the pattern if you're closer to one or the other and don't necessarily need to measure the veloicity to make the prediction.

Dr. Mann did much in his testing on vibration and points of impact, but I don't remember if he published anything on the repeating patterns as velocity changed.

I wonder, also, if there is any research published from military sources - as they have a vested interest in such knowledge.