I may have misunderstood you here Malcolm I know it tapers wing section thickenss wise (thats where it gets dihedral from, right? The variation in thickenss&gt but if its a constant reduction in thickenss towards the tip it still should lie flat on the spar? I will have to show you guys a pic.

Ok this aint the actual pic but its a quick drawing I snapped up

The ruler lies flat for a portion then it all goes miffy