I was a mean GM, apparently!
I always thought that most RPGs suffer their Heroes for not applying their innate abilities(Stat Bonii) to random chance situations.
Totally correct for Half Soft Cover mods arranged by closest cover to the Firing (N)PC down the line to the original target.
If the total adjusted OB hits the Soft Cover range, that particular target gets the missile, instead!
For swarm fighting surrounding a target:
As above, for however many combatants are engaged against the single foe but the percentage chance of hitting a friendly would be reduced by the Firer's Stat Bonus(we used AG).
So, 2 (N)PCs fighting one another has 50% chance of hitting either combatant.
Firer has +10 AG Stat Bonus so we skewed this by that same number as a percentage bump in hitting whom you wanted =now, there is a 60% chance of hitting the proper target in a pitched melee contest vs your friend - still not favourable odds!!!
For the OB used:
I'd make the friendly target be hit with Surprise at normal OB if the random chance did land on them.
I didn't like how the already released arrow had second thoughts about how hard it was going to hit someone that was not the intended target!
It made targetting into melee combat something you really needed to be sure of and acceded to by those possibly in the line of fire!