This pattern I'm not very confident about, since I've only spent 7 months in the Mountain Time Zone, but if I compare a girl from a more traditional area and her clone from a more modern area, the traditional girl has a smaller ego about her looks. *
By "traditional," I mean a place where females fall in love, participate in courtship, explore physical intimacy, and get married by 25, settling down after that (whether she has kids or not doesn't matter in this case). Then "modern" is a place where females keep themselves in the dating and mating market past 30, often until 40 and beyond. Let's just be clear that "traditional" describes the social environment she inhabits, not any property of the girl herself.
Here is a simple model to account for the smaller ego of the traditional girl. Girls are not born with knowledge of their attractiveness level, so figuring it out is a learning problem. Since you're only as attractive as everyone else says you are, this is a social learning problem. Your two sources of info are the responses you get from guys -- the more attention you get, the more you increase your rating -- and an assessment of your female competition -- the more you stand above the average female, the more you increase your rating.
Since I'm not concerned with really building a formal model, I'll just assume that a girl starts with an initial guess that is below her true value (since girls tend to be overly self-critical about their looks when they're teenagers), and that each episode of social interaction adds or subtracts a very small amount from her guess, as an tweak or update. Let's say she starts getting this feedback at 18, when she can go out partying, and that it ends when she's 25, the age by which most women get married or at least drop out of the dating and mating market. Concretely, let's say she goes out only one night a week for 50 weeks per year for 8 years, and she updates her value after each night out, yielding 400 updates of her value.
Now, imagine what happens to the same girl raised in the traditional and modern environments. In the traditional area, the other females who go out (not necessarily to nightclubs, but anywhere that people looking for dates and mates go) are more or less her age, the post-25 women having largely dropped out of the market. This affects both sources of feedback: since the males are viewing a group of females who are nearly all 25 or younger, a PYT of 22 years doesn't stand out as much as she would in the modern area, whose dating and mating market is much more heterogeneous for age. So, she gets more male attention in the modern area.
Moreover, since she competes within a group that has a much higher average level of attractiveness -- girls in their early to mid 20s being the most attractive -- the girl in the traditional area doesn't see herself as "standing out" as much from her peers, compared to how she would perceive herself in the modern area, where half a nightclub might consist of women over 25.
Let's say the effects of the modern area add an extra 0.0025 points to her value each night, on a 1 to 10 scale of attractiveness. ** Then after 400 updates, her self-perception will be a full 1 point higher than the self-perception of her clone in the traditional area. I'm obviously not trying to be very rigorous here, either in the choice of model (which should probably be a diminishing returns function, rather than a linear one) or the particular numbers. This is just to give a rough feel for what is going on.
Awhile ago, I suggested something similar for why pretty girls from better looking countries are more humble: they are comparing themselves to a higher average, and the men also apportion their attention based on this higher average. The same logic is at work here, only now one area is better looking because the less attractive, older females have removed themselves from the dating and mating market and are "out of sight, out of mind."
This has practical value, since it suggests making a trip to a more traditional area to pick up your girlfriend or wife, or even if you're only after a one-night stand. Pretty girls just won't think as much of themselves as they will in a more modern area. Also, it means that you won't have to "neg" as much, since that's only supposed to take a big-ego girl down a peg. Most guys would love it if circumstances allowed them to act more human and less calculating around pretty girls, after all. Add this to the previous advice to go to an area with a high average and high homogeneity, and you will find yourself courting a stunning rural Sicilian girl like Michael Corleone did -- just make sure you don't piss off the mafia and get her blown up.
* It's important to compare similar girls in different environments. Taking the average level of humbleness in the two areas doesn't tell us much.
** The most that the extra points could be is 0.025 -- imagine a 0 gaining the maximum 10 points due to living in a modern area, and divide this gain by 400 updates. So, the example assumes 1/10 of the maximum per-update gain. I could drive down the assumed extra points by assuming that she updates her value more than once a week, which seems likely.
Say she updates her value every day, based on how guys treat her throughout the day and what females she sees when she's out and about -- females who suggest that they're in the dating and mating market. A 40 y.o. woman with sweatpants and a stroller would not enter into her update, while a 40 y.o. with a $150 haircut and tight designer jeans would. Here, for the modern area girl to end up 1 full point ahead of the traditional area girl, each update would only need to add about 0.0003 points -- an order of magnitude less than what I assumed above.