As more "experts" chime in about the factors that effect forward lean, it becomes clear as mud that FL is almost impossible to nail while trying on boots in a ski shop.
I attempted to explain in my first post that there are definitive measurements and assessments that all boot fitters can learn to do and learn what factual adapting changes you can make to a ski boot with predictable and provable results. Then there is fore/aft balance which is the honey hole of unpredictability based on so many malleable and free flowing possibilities and combinations of complex movements and compensations that prove again and again the premise why even God cannot hit a one iron.
Lets throw out some of the parameters that cannot be assessed relative to Fore/Aft balance.
Strength
Flexibility
Coordination
Proportions of your frame, as in combinations of length of torso versus length of lower body, versus length of lower leg to proportions of the femur, hip socket width, angle of the femur into the hip socket, etc, etc, etc, and etc...
Size and shape of the calf and lower leg
Inherent performance of your bodies gyroscope that controls balance
Hand eye coordination
Foot size relative to frame size
Innate propreiception of moving your body through space at varying degrees of speed and gravitational pull.
Why these above factors are so different than the internal fit, ankle range of motion, arch flexibility, and forefoot mechanics, is that those inside the boot factors are mostly "if / than" problem solving. Meaning that when you know what the ankle ROM is you can make a definitive change in the boots net forward lean that is based on physical commonalities that can be discovered and repeated with every skier. With Forward Lean or binding Delta, there are too many variables as stated above, without definitive repeatable "fixes" to make hard and fast "rules" to be used. Stripped down it means that to find home base, if it is not inherently correct out of the box, is a game of testing the parameters on snow with a few shims and parts to be able to test in an "on / off" method like increasing binding delta, taking a run, then decreasing binding delta and taking a run. In most instances this form of testing shows the trend of the direction that will work best for your skiing. The same could be done with a forward lean wedge, by testing it in the back behind the calf, or reversing the placement at the top of the tongue, or removing it all together.
A good boot fitter can do all the basic work necessary to get you out on the mountain to begin the process of discovery of the best fore/aft balance while skiing. The last 10% of the process can be discovered on the mountain by increasing or decreasing the FL formula, and or increasing and decreasing the binding delta. The numbers are millimeters not inches.
It is also worth mentioning that the process should exist to find the sweet spot to begin and end your positioning in every turn. One of the reasons that the concept of FL balance is so misunderstood is that a vast majority of skiers believe that the boot should be like a cast that should be set-up so that you are being controlled by the angles of the boot. This is a false perception as the boot angles need to allow the skier to adapt to all speeds, all gravitational pulls, all snow conditions, on all skis. To this point you can chase this mechanical concept that the boot does all the work not the skier. The solution in some instances is some coaching or a lesson to help the skier learn that this magical balance position is a fluid and moving target that needs to be supported by the boot, but not mandated by the boot. Your propreiceptive ability to re-center your hips and feet over the middle of the ski between turns is a skill that can be taught and trained into any skiers technique.