Hi Michael,
I was curious about how you move the plane of focus with this setup. Do you move the whole unit, move the front standard, or move the rear standard. It seems to me that any of these options presents problems. If you move the whole unit, the your perspective changes. If you move the front standard, then both perspective and magnification change. If you move the rear standard, then perspective remains constant, but magnification still changes a bit.
Is this just something your stacking software handles for you?