Another thought I am having regarding the kick is that in butterfly and breaststroke the short axis rotational pulse is followed by the kick. Should we not do the same in TI freestyle. Whereby the core drive is a split second before the kick, rather than the other way round?
This seems to make sense. After all, the dolphin kick and the flutter kick are close relatives. In theory if you can do one of them you can also do the other and they are both supposed to come from the hips. I have found that swimming front crawl with a dolphin kick is a good way to find a good rhythm for the two-beat kick and although I haven't tried it I guess that fastening your ankles together with a band or inner tube or similar would be a good way to practice this. I know that this done in some quarters. I'm not sure that it would be very different from just holding your ankles together - perhaps there would be less tension in the leg muscles, which would be a good thing.
Today I swam 500m front crawl ( 20x25m) concentrating on a six-beat kick and was quite pleased with the results. I then did some vertical dolphin kicking, which I find quite strenuous. One minute is a long time for vertical kicking, I find. I'm sure Michael Phelps can do five or ten minutes at a time holding a heavy weight over his head, but he's young and fit and has been doing that sort of thing since he was a boy. Still, on a smaller scale, we ancients can emulate the greats.