Instead of just getting more stacks when casting Flow, Id rather some type of proc chance. Example.

SCH - Trait that gives Physic, Adlo, Succor a 5% chance to gain 1 stack up to your max of 3
SMN - Trait that gives Ruin, Ruin2, Miasma a 5% chance to gain 1 stack up to a max of 3

Not to leave WHM out

WHM - Trait that gives Cure, Cure2, Medica a 5% chance to lower the CD for Shroud by 10-15s
and/or change shroud from 80 Potency over 15s to 1% Max MP + 80 Potency to scale a little better.