Resilience is a quality within the person. Severity of the stressor and length of time of the exposure are factors that are external to the person. All three factors affect the degree of trauma the person experiences and the severity of PTSD that results.
Your inquiry raises new valid theories that have been set aside due to defining PTSD within the realm of cognitive stress. Yes, I agree with your correlation. That if you also correlate the region of origin with military culture in the region. Resilience is definitely part of military culture and responds to regions. An interesting matter to be investigated.