I don't think the exact penalty is known, but I can tell you from my own experiences with shooting on both corsair and ranger that it's negligible. If your gear sets are up to date you won't even notice the ranged accuracy penalty. Anything I can hit at optimal range I can still hit reliably if I step back a dozen or so yalms. The ranged attack penalty is more noticeable than the accuracy penalty if you ask me, but good attack buffs can overcome that too. Your gear sets should still be the same whether you're at optimal distance or shooting from maximum range 25 yalms away.