I think that's a good approach, reverse engineer the hammer (or strike weight) based on a targeted Front Weight. My own midline is 85% of the published FW maximums that produce a balance weight of 38 grams. That's a bit less than what you've posted as your midline. Where that needs to deviate is in the case of concert instruments that sometimes want heavier hammers and one draws a limit to how low you want the action ratio to go for reasons of regulation. That 85% number is very close to what you get in the Fandrich and Rhodes ("Actions to Die For), btw. Also I'm not rigid about following that specific target as you move up into the high treble as long as the strike weight curve is smooth.Most of the inertia in the system comes from the relationship between the action ratio and the hammer weight. The key provides only about 30% of the total inertia, some of that is the lead, some of that is the keystick itself. Taking a lead or two out of the key stick doesn't impact the inertia that much. Changing the relationship between the hammer weight and the action ratio does. The wippen contributes virtually nothing to the overall inertia.As suggested, a simple way to establish a targeted hammer or strike weight curve is to remove the key(s), install or remove enough lead to get the Front Weight to the desired 85% of FW maximums target (I usually do this with C3, C4, C5 initially) and then mix and match shank configurations with sample hammers until you get the desired balance weight. Use those sample hammer weights to establish your strike weight curve. As I mentioned, I am pretty careful about not exceeding my strike weight curve down through the bass but if the upper part of the piano wants to deviate on the heavier side I don't worry about it too much. The inertia in the upper end will always be lower than the inertia in the lower end because the hammers are always lighter.While there are many programs that will calculate all this for you this simple method does get you on target very quickly.It's worth noting that the force to overcome inertia is some 20x greater than the static weight (DW) and so making sure that the inertia stays within a range is much more important than the static downweight (as DS points out).