For what it's worth, I rolled this out (d8+3, plus d4+3 x2, all at +5 to hit vs AC 13) and killed an orc 4 times out of 10. Damage totals were 15, 25, 7, 4, 14, 15, 10, 11, 16, 10.
But let's not get too hung up on the "two orcs" scenario. The whole point of AoEs is that whereas normal attacks get worse as the number of attackers increase, AoEs get better. If the monk is facing 2 orcs, the whole party is probably facing 8 orcs, right? Find the biggest cluster you can and nuke it as hard as you can.