I accidentally erased a long post a few days ago and haven't had the heart to fully recreate it. But taking a half-hearted stab at it....
Population density of humans depends on a lot of factors including how efficient agriculture is and what food crops they have available, how recent the last epidemic was, and how often there are major wars.
And in fantasy worlds, how dense the population of non-humans is and how aggressive they are plus the population density of aggressive creatures which might want to snack on humans.
Out of those factors, war is probably the most important. It directly reduces the population while disrupting food production (which directly and indirectly reduces the population) plus displacing people so diseases spread more rapidly from one community to the next...and continue to spread rather then burning out (which directly reduces the population). The more recent the last war, the smaller the population in the warring kingdoms AND in the surrounding kingdoms (reduced food availability and refugees spreading disease).
In a typical fantasy setting, you aren't going to find a lot of lone pioneers out in the middle of nowhere with just himself and his family because it's much too dangerous.
So the next question is how safe would it be to live in a small village of say 20-35 people? There could be a hell of a lot of villages of that size in the area you're talking about. But if that's too dangerous, there won't be any.
The larger the town, the more amenities are available (tavern, temple, mill) but the more opportunities for disease and crime. And the larger the town, the fewer farmers per capita since farmers would have to walk out to their fields then return and there's only so far a person can walk and still put in a meaningful day of work.
So if tiny villages are plentiful and farmers turn out way more food than their own families can eat, towns and cities could be huge. But if you assume fewer but larger villages and relatively unproductive farms, cities would be smaller since there would be enough food available for import to maintain their population.
Personally I prefer GMing with large villages and small people per square mile. Lots of ruins ranging from abandoned small villages to more profitable ruins. Lots of monsters. Cities which are the size of a large modern town and no cities which are the size of a modern small city.
But I dislike GMing political intrigue campaigning and like the players being able to get their PC's out away from a lord if I screw up things and GM myself into a corner.