Your a glutton for punishment, since a 10.5" barrel has very little bore after the gas port; making it ammo sensitive as hell.

So before you touch the gas port, pick an ammo and stick with it. Hence even 55gr ammo from differant manufactors will cause problems with the 10.5" barrel.

As for lightened carrier parts, this will cause the B/C to unlock faster, meaning will need a smaller gas port than normal isntead.
Also, adding a suppressor or even muzzle Brake like the KX3 will increase bore back presssure, meaning even a smaller gas port as well.

Since I don't have a clue of what specific ammo your going to run, or what is going to be attached to the barrel like FS/Brake/Supressor, can't give you a idea of gas port sized needed for your starting point.

Doesn't matter, since your still dealing with a short amount of bore after the gas port that still have to pressurize the piston assembly correctly as well.

Get the port too large, and the bolt is still going to unlock too soon to cause short stroking problems.

As stated, the 10.5" barrel is going to be ammo sensitive.

Not due to the over all working pressure of the round so much, but the powder used, and what gas port pressure is going to produce isntead.
Hence the slower burning the power being used for the round (max spike pressure from the chamber distance), the more gas pressure that round is going to produce at the gas port.

So in this graph, we are using H335 at nato pressure of 60K,


If we lower the working pressure of the round to 223 at 55K psi with the same powder, decreases the gas port pressure.
If we use a faster burning powder that H335  to 60K, pushes the pike to the left and decreases the gas pressure to the port as well.

So of the ammo listed that you use, one was nato pressure, two where 223 pressure, and the steel case poly coated ammo, having a higher adhision to the chamber during extraction as well.

Myself, before touching the gas port, would go through the rig to try weed any problems out with possible gas leaks in the gas system to begin with. Hence block to barrel, key to block, and even key to carrier if it has a slight leak. Also, would scrub the chamber clean, then take a look at the chamber to make sure is smooth as a mirror, or if it need to be lapped polished if possible instead.

Then at that point, would settle into an ammo type, tune the rig for that ammo to run the rig alone.  Short of that, there are muzzle brakes like the KX3 that will add a touch more bore back pressure, to make the 10.5" barrel act like a longer barrel to be a touch less ammo sensitive instead.