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In the case of the Tiger from Tiger Chess, the author didn't use the word "forward" but "outward" instead. In my opinion, with that word the definition is clear and not really ambiguous.

With the understanding that direction specifications in a continuation leg must be interpreted in an orientation where the basic leap of the previous leg is 'forward', outward and forward mean exactly the same: continuation in as much the same direction as possible, given the difference between the leaps. But I think there would indeed be no ambiguity if K/Q-like atoms in continuation legs are avoided. For [N-Q] 'outward' would be ambiguous, as it would require some advanced geometry, which most people would not master, to decide whether the adjacent diagonal or the orthogonal continuation had the smallest angle with the N leap. In fact, after a C leap a W continuation would have the smallest deflection, while the F continuation would bring you at the largest distance from the square of origin (because F steps are geometrically larger than W steps), and both could claim to be 'outward' on that basis.

The point is that a general system must also be able to account for cases where the continuation is not the one that goes most outward, and there aren't enough spare lower-case letters to build a completely alternative system for indicating arbitrary relative orientations. So we will have to do with the familiar f, b, r and l, also in continuation legs. This doesn't seem a problem; even on one-leg moves 'forward' is to be interpreted relatively, namely w.r.t. the player.