I must have missed something: did Barbara say that design A would be difficult/impossible to pleat to the sett?

My answer to that would be that pleating to the sett isn't necessary or even preferable in my opinion. Tartan A could be "pleated to the block", to the open green area, for example.

Which brings up an interesting issue: in The Art of Kiltmaking "pleating to the block" isn't mentioned. What is mentioned is the "unfortunate lawnchair effect" of having horizonal elements predominate.

But this sort of pleating is rather common. Some military kilts and many Pipe Band kilts are pleated that way. It's not always a clear-cut thing, because kilts can be pleated to the stripe, but to a stripe which is very weak, so at any distance the kilt appears to be pleated to the block.

In any case I wouldn't reject a strong tartan design simply because it doesn't lend itself to one specific style of pleating.