Yes I think it is under gassed. My 18 mid length gas Faxon Group Buy barrel port is .076. Changing to a lighter commercial bolt carrier and improving function really points to an under gas system. As the rifle and magazines wear in reliability might improve. With the ejection being 3-4 o clock sounds more like under gassed. I have seen three or four over gassed 6.5 Grendel rifles and the brass almost always went to 1 or 2 o clock.
Shooting fully loaded higher capacity mags can add drag to the bottom of the bolt carrier which requires more momentum to over come. One concern for an under gassed firearm is in cold weather. Temperature can affect pressure. In hot weather your firearm might cycle the 90 grain load but it might short stroke at 0 degrees. I like how my Faxon 18 mid length shoots and it seems like the gas is well regulated with a .076 port. (No Suppressor)
If you decide to measure the gas port you can use drill bits to help get an idea of the port size. It wouldnt be the first barrel to leave the factory with an under size gas port.
Shooting fully loaded higher capacity mags can add drag to the bottom of the bolt carrier which requires more momentum to over come. One concern for an under gassed firearm is in cold weather. Temperature can affect pressure. In hot weather your firearm might cycle the 90 grain load but it might short stroke at 0 degrees. I like how my Faxon 18 mid length shoots and it seems like the gas is well regulated with a .076 port. (No Suppressor)
If you decide to measure the gas port you can use drill bits to help get an idea of the port size. It wouldnt be the first barrel to leave the factory with an under size gas port.