I'm interested in the results of your tests!
A couple of quick tests in VIP:R 0.301 has led me to believe that this lack of pop mobility depends on (at least) two things.
1. The life rating of the province
2. The "amount" (for example: "5.0", "2.5", "0.8" etc.) of the province RGO
Initially, during gameplay, I noticed unassigned pops to be unwilling to leave provinces with a life rating of 25% or less. In my test however, I found that pops willingly left provinces with even lower life ratings (24% for example). I also found provinces with higher life ratings (like 28 or 29%) where unassigned pops just refused to leave. A mystery? Not when you combine life rating with RGO "amount". I'll just skip to the math...
I found that pops happily left a province with a 3.5 RGO and a life rating of 28%.
3.5 x 0.28 = 0.98
I found that pops wouldn't leave a province with a 3.0 RGO and a life rating of 28%.
3.0 x 0.28 = 0.84
So unless there is some sort of table for this pop behaviour like for assimilation I'd guess that this depends on life rating and RGO "amount" with the breaking point somewhere between .84 and .98 (when multiplying like I did).
It also seems this has nothing to do with RickRand. Except that I guess most people would not find themselves with shiploads of pops in low value, low life rating provinces without your, once again, excellent contribution to Vicky :rofl: