you're looking at it wrong for the discussion KN
think of it by voidstone count. each character uses 1 voidstone and shares the same spawn point and spawn time. so his efficiency goes up x 6 with amount of spawns required per pouch.
it's not about counting the rolls given. it's about boosting the efficiency per NM spawn.
It's the same method of going into a group of 6, and, after everything is said and done, having 5 characters trade all the good ***to the 6th.
It doesn't work for everyone. Not everyone can or wishes to 6-box.
You aren't increasing the rate of the drops, you are giving yourself more chances (aka "rolls") of the drops.
You might as well 18 man the pop if you want true "efficiency" then.