The added lead to compensate for a high strike weight ratio isn't the main driver of high inertia. It's the mass of the hammer combined with the high ratio that is the problem. A 5.9 SWR calls for a lighter hammer to avoid high levels of inertia. A 5.4 SWR will perform differently and will accommodate a somewhat heavier hammer.Inertia is the main event for touchweight dynamics. The DW associated with any BW setting simply represents the minimum force required to actuate the key. The force required to accelerate the key to its maximum velocity can be some 20 times the force required to simply get the key moving. But what pianists feel is the resistance to acceleration more than the static balance weight, or down weight. Complicating things is that we don't play the key in the same position fore and aft which affects the SWR and thereby the inertia-as well as the BW!
it's probably not worth laboring over smooth FW versus uniform BW. Various techs do it both ways with perfectly good results. In your case, trying to have a smooth FW with two different SWRs will be impossible, though you can smooth each the sharps and the naturals separately.
But the dynamic differences between the naturals and sharps is already there even if the SWRs are the same owing to differences in key length. Of course you can have two different capstan lines: one for the sharps and one for the naturals to correct that if you want to do that.
Pick your poison.