If she's functioning correctly, you really don't need to do anything. Variances in ejection angle are typically due to variances in gas pressure, as gas pressure dictates bolt carrier speed. If you're too "over-gassed," you may not have a function issue, except that you're dumping more crud into the bolt carrier and receiver than normal and putting more stress on the parts than necessary. Sometimes, too much gas can cause the case to hit the case deflector (if your receiver has one) with enough force that the case bounces back into the ejection port and stovepipes. I had that condition with a recent AR. Too "under-gassed" and you either don't eject the case at all or the bolt doesn't cycle far enough back to pick up another round from the magazine. In general, the higher the gas pressure entering the gas key, the shallower the ejection angle (closer to straight ahead)... 1:00 - 3:00 ejection. The lower the gas pressure the wider the ejection angle -- 3:30 - 5:00 ejection. I prefer a consistent ejection angle of around 4:00 because I know I'm getting enough gas pressure for reliability yet no more than necessary for reliable function so that I keep carbon buildup minimized.
This is why I like an adjustable gas block. With just the turn of a set screw, I can control the amount of gas reaching the carrier. When initially setting up an adjustable gas block, just barely crack open the adjustment set screw and load 1 round, nothing else in the magazine. With the setscrew closing off the gas port, you should see the bolt fail to lock back on an empty magazine. Slowly open the adjustment screw a little at a time until you see the bolt properly locking open on the empty mag, indicating you now have sufficient gas for function. Now open the setscrew another 1/8 - 1/4 turn or so to ensure consistency. At this point, you should see your cases ejecting between 4:00 - 5:00. The bolt and buffer assemblies don't take as much of a pounding when setup this way.
