Until there's some benefit to having lots of knights, realms will always strive to spread their nobles across as many regions as possible. The more lords and fewer knights you have, the more gold there is for everyone on tax day, and since a region can achieve maximum everything with one noble just as easily as with 3, there's absolutely no reason for a realm not to spread their nobles as thinly as possible.
The most stable realms, and typically most powerful, have just above 1:1 nobles-per-region. Morek Empire had exactly 1:1 on March 1 (the beginning of the monster invasion) and has maintained an average of 1.2 nobles per region since then.
Currently the 4 lowest density realms are: Morek (0.9); Astrum (1.3); Fissoa (1.5); and Swordfell (1.6). All 4 of them have about the same number of regions today as they did on March 1, give or take 3 regions. The 4 highest density realms are Asylon (4.7); Barca (4.0); Luria (3.6); and D'Hara (3.2).