I'm not sure what all of this means . . . but the measurement to the sparkplug is made perpendicular to the wheelbase measurement, not from the actual location of the sparkplug angularly to the spindle (or whatever).
I've seen front-to-rear bias weight measurements with differing engine placements -- and i believe engine placement definitely should not the determining factor in engine selection. Moving the engine an inch or two make very little difference. There're a whole lot of other components that can be placed in differing locations to get the break you're looking for.
This ain't Formula 1.