Ummm....overboring the hole in a very well researched and tested and tuned muzzle brake like the Y comp will only serve to ruin it's effectiveness. The phantom, too.
Just as you described, every muzzle brake that you open up too much will send more of the blast out the front instead of where the muzzle brake is supposed to send it, out it's carefully machined and precisely placed ports. Open the hole, and more gets by the bullet instead of being redirecetd out the ports at high velocity, thus lessening recoil and keeping the muzzle down, but as a side effect redirecting some of the blast back tword the shooter.
Go ahead and open it up, you'll have a very nice, expensive muzzle weight/boat anchor, but a very crappy flash hider or muzzle brake.
Unless you're an engineer that understands the dynamics of ballistic air compression or the thermodynamics of smokeless powder combustion, leave the modifying of these things to an expert.
The Phanotm has been recognized for a long long time as one of the best flash hiders in numerous formal and informal studies, on par with the vortex. Same thing with the Y comp, it's pretty darn good at helping keep the muzzle down.
One other thing to think about with the dimensions of the A2, it was designed for WORST CASE exposure to the elements and battlefield conditions while still providing some measure of flash supression. Soldiers universally use, abuse, and neglect their arms, especially when they're in the shit and there's not any time to clean and maintain it. The larger clearances of the A2 reflect that, as does the issuance of a shoot through muzzle cover!!!!! Are you willing to sacrafice the overall effectiveness of your FH on a percieved need to keep things out of it, or are you more likely to end up shooting at the clean range, with clean ammo, transported in a clean vehicle, where it comes home and gets cleaned after every range session? Me, I shoot high power matches in the dirt and in the rain. Never plugged a muzzle yet in 8 years.
Looks like you've found a solution in search of a problem.