@J.Sallé Remember that a tacit function (like all functions) is either called monadically or dyadically. The type of calling also applies to every other function, beginning with the rightmost. (The ones in between are always called dyadically, and if there is one left on the far left, it is always called monadically.)
So for a b c d e f only c and e are always called dyadically. b, d, and f are called in whichever way the whole function is called. a is always called monadically.
