Just some rambling thoughts:
upright stance is affected by "forward lean" of boot and "delta angle" of binding. ramp angle does not affect the lower leg angle.
a boot could have a over 20 degrees of forward lean yet if there is a negative delta angle the skier could be in a more upright stance even though their net forward lean was quite radical - OR - a boot could have 10 degrees of forward lean and the binding have a steeper delta angle and the net result would be the same.
Point being, forward lean does not neccessarily dictate how upright a stance is. When discussing an "upright stance" we need to look at forward lean of the shaft as well as delta angles to get a true picture of the "net shaft angle".
I don't know if my methodology is ideal but... I usually look first at my dorsiflexion related adjustment needs and try to create a net forward lean angle that matches a 50/50 distribution of pressure ball and heel when standing barefooted on a level floor. I don't know the exact biomechanic reasons, However; it would seem to coincide with gregfits post in another thread on dorsiflexion, which stated that he believes the achillies tendon needs to be "prestretched" abit to optimize balance. My method is not an exact science but the skier will migrate to a position that feels comfortable and distributes the weight fairly evenly. I then measure this angle and try to recreate it inside the boot by adjusting the ramp angle and the forward lean (if possible).
Once this angle of the ankle is established I look at the skier in the system with boots on and clicked in their skis. Using the preliminary plumb bob from the knee to the boot toe target, I will adjust the delta angle by plating the boot sole with differing thickness plates and/or shimming under the bindings to achieve this relationship.
Using this method, a shorter tib/fib'd person will not have as upright of a stance as a person with a longer tib/fib. Though the final adjustment is not decided until some dynamic testing can be performed on snow, this gets it in the ball park.
I would think if one gets their boots too upright they will probably need a leverage advantage of a heel lift or increased ramp angle in zeppa to compensate. The combination of an upright boot with a flat ramp had better be pretty soft unless your binding has alot of delta angle (ie:Look, Rossi), I would think...