what should one watch for as far as gas-block adjustment ?
stagpanther probably answered as best as can be done without one actually being their looking at the rifle, knowing the load, etc.
Almost all Large frame ARs are significantly overgassed. The shorter the gas system in relation to barrel length, the worse it is.
Checking brass rims and even case bodies for extraction issues is first. How far the cases get thrown is next, but that is as much the ejector as the bolt carrier velocity.