It's a good question. It's hard to tell if that really puts you at greater risk. What you're describing is a situation where there is repeated exposure to high trauma. That in itself is a risk factor.
But I think at the end of the day it's an interaction between your personal biology and the environment you get exposed to. As for what it is inside of you that makes you resilient or vulnerable, we still don't understand. What we do know is that repeated trauma is a factor that results in PTSD, so that's the issue.
What you're describing is true in a way because in a smaller community you are more likely to be the first there and to be responding to many more traumatic events than you would if you were in a situation where the pool might be larger, where the population might be larger and you might not have as much exposure to trauma per person.