Perhaps you can leave that number ["Q": ballast*draft/weight] as an indicator of reserve stability and can get another formula to initial stability. That is not going to be an easy one because beam increases a lot initial stability. I have no idea of the factor but I am sure that a simple multiplication will not be enough (not even close) to account for the initial stability provided by the increase in beam.
To complicate things, more ballast and a lower ballast also increases initial stability even if in a much more moderate way.
To find a formula that will integrate all these factors will not be an easy task and will require a lot of work and a constant match with reality, using reference boat data to see if the formula works.
A problem which appears in all kinds of fields is that people are always wanting to reduce multidimensional things, or even curves, to single numbers. This fundamentally can't be done.
But that isn't to say we couldn't in principle anyway have a small set of numbers that would give us good approximation of the overall picture.
In practice, actually getting this from the manufacturers is probably beyond hope: one can't even get minimum sailing displacement let alone design sailing displacement in most instances.
But in a dream world if we had:
A) Resistance to heel at zero degrees, divided by sailing displacement
B) The designer's value for optimum heel angle at some condition, and resistance to heel at that angle, divided by SD
C) Resistance to heel at some standardized angle that people would find intuitive, say 45 degrees, divided by SD, and
D) Energies required to capsize from angles B and C, divided by SD
Then that would give a pretty good handle.
Chance of them all giving us these? None.
We can probably get A, and with curves we can figure D from any angle we like, if we had sailing displacement.
In the meantime, ballpark ideas are all that is possible probably though I've seen you've done a great deal of work on it.