I treat '&' or "a" takes beat value from its immediate previous beat all along despite I thought if time allows, triplet or other expression may add more color in the presentation;
varying count of tatata... are better in personal character.
Now another version is that it takes time value from the immediate following beat more often , I felt confused because of that use this common rule we still can express what we want to accent or speed up .
I think , I must ignor or not understand something very important when I tried to solve this problem, such as dance style, music phrase or the figure of preceding / following . personal favor / ability ? Help.Thanks.