I think when calibrating alignment, the stacking distance is irrelevant, so one can use the full travel distance to calibrate it. In this sense, the merit of your method is obvious -- if the white paper is far away, say a meter or more, the shift of laser dot (or line or cross) will be significant enough to show the difference.I do recall meeting some frustrations with this approach, such that I didn't think my method mature enough to post out. But as it's been a few years, I don't recall what those frustrations were. I do think the approach has merit.
In other words, if there is misalignment, the shift will be heavily biased toward the misalignment, so even if you have rail shifts, the end result will show the bias, statistically speaking.