[Build help] Ngamahu's flicker strike chieftain

I'm building a Ngamahu's Flame axe flicker strike build with the chieftain ascendancy, using blood frenzy to keep up frenzy charges while doing general clearing. Damage is awesome, clear speed is awesome, only issue this build has is sustaining frenzy charges while killing bosses or tankier rares like the red skulled beasts.

Any ideas on how i could sustain frenzy charges better?