Aside from possible bugs and some missing UI informations, I guess it is hard to find a suitable base migration value.
If it is too high, there is no necessity for the player to invest in multipliers to increase this value by techs, buildings, traditions, etc. (PS.: The Advisor veteran trait "Frontier Spirit" got buffed with +% automatic settlement chance too). It also devalues manual resettlement and its connected traditions and species trait (costs, policies and its implications).
If the the base is too low, even empires with low pop growth will eventually run into the problem of stacking civilians and any way to increase it might not even counter it.
Assuming it is working correctly, it should be possible to stack multipliers ontop of base migration high enough to be sufficient even for egalitarian clone empires, even if it costs you some effort.
No-one actually wants to invest in those modifiers though, they just make anything associated with them be weaker. Changing them into something more worthwhile would be a better solution.
In the mean-time, egalitarians get screwed over even more, since it's -20% happiness if you turn on re-settlement to actually make this supposed new growth system work in the first place.
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