Personally i prefer carbine length buffer system. Its more tunable than rifle length. Multiple buffer weights and spring strengths. Especially with an adjustable gas block id expect no issues. Id go carbine lenght with an h buffer and standard spring. Set it up and adjust your gas block. If your somehow still ejecting forward , instead of the 3 to 4 oclock position id add a springco extra power spring.
Im currently running a 6mm arc, kind of a sister cartridge. 20in barrel, rifle length gas, adjustable gas block, carbine length buffer tube, h buffer and a jp +5% spring. It was ejecting at 3:30 even before i tuned the gas. The springco blue +15% was too strong. Going to try a carbine buffer next outing and see what it does.