What struck me about Mace's description of how to tap your foot was that I'd heard it before - from the bellows piper Dick Hensold, who said the Baroque/ Cape-Breton fiddler David Greenberg had suggested it to him. The idea is that the foot keeps an unvarying pulse, but the downbeats you play don't exactly match it: you rush on or hold back for expressive effect, but the foot keeps track of how far you've drifted and gives you a reference point to go back to when you've made the expressive point. The description of both the technique and the reason for it were so similar over that 200-year span that there has to be a direct link (though perhaps Cape Breton fiddling has lost the doctrine of affects as a rhetorical framework? I wouldn't even be sure about that).