Seems to me that it would be simpler to change Noct shields into 'shields-over-time'.
Instead of a flat 500 potency shield for Noct Benefic, it applies a 100 potency shield every 3 seconds, which stacks. Noct Helios: 50 potency shield.
This would serve as an autoattack damage sink thats far more mana efficient, in addition to providing a decent big hit shield when used in advance, and extending buffs will increase its effective potency in exactly the same manner as the HoTs.