As the two settings imply, these are matchmaking preferences and not queue splits. The matchmaker will try to form an adequately balanced match based on parameters that expand as the time spent in queue increases, but simply if it cannot form a desirable match with these preferences then it will just go back to whichever parameters take priority in terms of how they are weighted. You can think of it as a region preference, although the matchmaker should prefer to match locally, under certain circumstances it may put you in a different region simply because it was the optimal match it found at the time the match was formed.
Obviously this is all up in the air and can be improved on Valve's end at any given moment, with no notice to us.