that setting just selected which peer cache to use, and the frontcode peer caches directed users to other primaries using the same cache, each region had its own peer caches so you would get connected to the same cache as others in your region so would be likely to connect to users in the same region.
That is no longer the case, firstly all region selections will point you to the same caches (
https://www.winmxgroup.com/check2.php for a list), and also if the patches were changed to use different caches for each region, the new caches locate primaries directly from the network so just give random primary users rather than other primary users using that cache.
in short, that setting is now as good as useless, it doesn't do anything