Good answers on this thread! I also got an A in college calc...so consider that contouring the frontal area actually increases the square footage...like cutting a square out of a ball and then flattening it out.
However this doesn't tell the whole story because even though the actual sq footage is greater, drag coefficient is reduced as a result of the contour. Further complicated by the fact that the actual drag created by the TT is a function of how much air is already being moved out of the way by the tow vehicle.
Vehicle manufacturers have already done the heavy math and distilled their recommendations down to a surface area limitation that we can calculate as simple HxW...getting into the short strokes on this won't materially change the answer. As Cramden said, if you're going to ignore that part of your owners manual, just do it, you don't need a loophole to justify your decision.