For single target, you don’t really need to change your rotation for the Mantle. It’s not really intuitive, but you don’t really end up using more Arcane Barrage by changing the rotation unless you use it during Arcane Power, which is a slight DPS loss.
For AoE I think that it would actually be a DPS gain to use Arcane Barrage more liberally even during Arcane Power. I honestly didn’t do a lot of testing on the simple rotation for AoE, but, some quick tests do show that you should use Arcane Barrage once you have 4 charges during AoE. I can add that to the rotation.