If possible, we should solve the problem of dependencies that become unfair because of the levy system.
When the armies are not raised, the dependencies suffer the penalty "power compared to that of the suzerain" (in French) and can rebel ...

It would be necessary, I think, to calculate the "power" of the nation on the number of recruitable population then to switch on that which is levy and to switch again on the number of population available for the levy. (So as not to distort the calculation)

Just a guess. I never did a mod :)