Who's influencing me right now: Roger SG Sorolla.
Roger over at Rolls, Rules & Rolls just re-posted these rules. I hadn't seen em before.
It occurs to me that they're ready made to drop into an OSRIC game. The attacker rolls to hit against AC 5 to AC 15 (DM's call; depends on the nature of the target) and compare the difference with the amount by which the target made their save vs. aimed magic weapons.
The rules for attacking into a brawl are the same for shooting arrows into a melee--in OSRIC, the attacker randomly determines their target. Speed saves are Saves vs. aimed magic weapons. I use 2nd Edition monsters, so size differences work unchanged.