geometry issues alone create a need to use an x stroke, to make sure all of the edge gets hones on every stroke, plus 3" stones are not all that common in the past, ie. thuringians and a lot of coticules, check them out a lot of 1 1/2 -2'" stones, just as mentioned, smiling blades need this to reach all of the edge, and just because your edge is a straight one , if the spine has geometry issues it causes the same affect.

plus your overthinking it, it works and has for a few hundred years I have one straight blade that has a warp in it, the edge really only gets honed as it approaches the edge of the stone on the x stroke, other wise on that side it would only hone the toe and heal, on the other side just the middle of the blade