DOH! After reading xausa's post it finally dawned on me the impact concern was side-to-side vs. drop. (Note to self: drink coffee BEFORE typing.)

I would think, absenting wind, it should be pretty much straight trigonometry. So, with a 70 meter zero, offset at 140 meters would be almost exactly the same as the offset at the bore. Other yardages should be close to a simple proportion. Probably not 'exact' in a careful scientific context, but certainly close enough for critters.