I have a different AR than yours, but I have had to deal with suppressor/over gassing issues. I'm not an AR expert by any means but I have built a few from the ground up so I might be able to help or at least pass on my successes and failures.
Background: Seekins billet upper/lower, 16" Rainier Arms Ultra Match 223 Wylde, SP3R V3 12" hand guard, mid-length gas system, JP Enterprises Adj lower profile gas block, yadda, yadda, yadda.
As far as I'm aware, the gas hole in a mil-spec barrel is the same from one to another. They are generally 'over gassed' to cycle not only different kinds of ammo, but also to overcome dirt/debris from combat use. The extra gas allows the carrier to push through the carbon, sand, dirt, etc… as well as more reliably fire a variety of ammo.
Once you add a suppressor, it causes resistance in the amount of gas that's normally allowed to escape with the round and it takes the path of least resistance (i.e. back to you via the block, gas tube, carrier, and in many cases through the charging handle into you face.
Arguably, the extra gas might cause premature wear of your parts, but there again, there are many ARs that have literally tens of thousands of rounds fired suppressed w/o an adj GB.
With that said, I decided to install an adj GB. I've had pretty good luck with JPs version. It allows adj via a screw. The more you tighten it, the less gas, and the other way around for more gas. At one point I was able to find a balance where I was able to get reliable function with the same gas setting suppressed and unsuppressed using LC 162 gr green tip. If you regularly switch ammo, YMMV.
Generally if you dial the gas setting down to fire suppressed to avoid 'gas face', if/when you take the suppressor off, there won't be enough gas to cycle the next round. It basically short strokes, ejecting the brass but it won't go far enough back to load a new round.
When I found my goldilocks setting, I marked it with a sharpie and used some Rocksett to keep the adj screw from backing out. You don't want to use locktite or similar stuff in this application because it won't take the heat that a GB will generate. Rocksett will.
All was good for @10K rds of flawless function but the last time I was out, I found the setting had changed…I'm assuming from the recoil…and it essentially became a single shot. I'd fire, the bolt wouldn't move, I'd pull the charging handle back ejecting the spent casing and loading a new one, fire, repeat….sucked!!!
To get through the rest of the day, I backed the screw out ensuring reliable function, but pretty much went back to over gassing the gun. It definitely changed the recoil impulse and wasn't as smooth, but it worked. I haven't had the range time to find that balance since.
Backing up a bit, the reason I bought the JP version is that I ran into similar clearance issues that you're concerned about with my hand guard. I would have loved to have gotten a Noveske switch block (lever adj), but the profile was too high and it comes preinstalled on the barrel. Even if it would have fit the next issue is that the GB is under your hand guard so unless there's a cut out in your hand guard you can't access the lever. As it is on the JP version, I have to access it from the side between the vent holes with a fairly long allen key. I keep it stored in my stock JIC.
I've heard good things about the Syrac system. At least it allows the ability to lock your setting down without the use of 'glue'. I have yet to try one though so I can't speak from personal experience. Profile-wise it should fit under most hand guards. You may run into the same access issue(s) if you ever want to switch gas settings based on ammo, because you have to access it from the front or squeeze an L-shaped allen key between your hand guard vents from the side.
Ideally, you'd want something with a lever or dial with multiple settings. Downside is that I'm not aware of one that will fit under a low profile hand guard unless you dremel an access channel into your guard. Even with that your optic, BUIS or something else might be in the way for top access.
Of course the other option is to get a shorter hand guard that exposes your GB. I'm not willing to do that yet.
Hope this helps.
