If your extractor has an insert, you could try removing it, or a different (lighter) spring, but don't F with the extractor claw. A too strong ejector spring combined with high bolt velocity is probably the culprit. The adjustable gas block will take care of the velocity. That may be enough.
Try this: Coat the face of the deflector with something that will transfer onto the case. I recommend Dykem. Manually and quickly extract cases from the chamber (this is to test whether the ejector by itself is causing the strike) and see if they are still hitting the same place. If so, then the gas block won't fix the problem. It will slow the bolt down, which overall is good, but if the cases are hitting at manual velocities, the ejector spring is the cause.
Adco sells a bolt dis-assembly tool to make this easy.
Unfortunately, I don't know what spring to use. DPMS doesn't have one on their site. Which might mean it is an AR15 spring.