if you use ControlClick, the coordinates, by default, are relative to the target window / control. This works on multiple monitors as AHK doesn't care where the window is.

This should simplify your equation a little as you can derive a multiplier for the coordinates based on the ratios of the axes of the relevant windows.

Src Max X / Dest Max X = divisor
e.g.
100 / 60 = 1.66r

then divide the X coord by the divisor
e.g
33.3 / 1.66 = 20.06

as you could define the divisors for each axis of each window on script load, this should greatly simplify things