Ar handguard length input please

[oregonshooter]

I'm 6-3 and long armed and had the same setup and found the 13" alpha too short for a fully extended thumb over.

If your barrel will allow it, get the 15" for this setup. You can always mark your barrel and "estimate" if it will work for you. Totally dependent on the user IMO.

The above was with a SOPMOD extended out 2 notches. I'm running my stock 1 notch in from full extension now but using a FSB and ff 7" DD rail and no thumb over grip now.

You might try running the stock out if you don't already. It would make the 13" work I figure. I didn't think I would like the stock extended shooting but can see now how it does keep your head up and more natural to mount the gun.