I would like to suggest that the 'Arcane Concentration' buff called 'Clearcasting' to have the capacity to occur and stack twice within the time limit of 8 seconds prior to its initial occurrence...
Please allow the Arcane Concentration buff of Mages to be able to occur not just once, but twice, within 8 seconds... and with the capacity of the buff to stack twice on itself as well. This means that Arcane Concentration has the chance to proc a second time within 8 seconds after an initial proc of the buff, and not exceeding a third time within the time limit.
This would work quite well with mage spells that cause several hits on a target within one spell cast or channeling, which are basically just the Arcane Missiles, and Icicles.