4p is definitely not working, tryed with ES and CS, the buff is there but the damage isn't increased.
Fel cleave trinket seems to be far better then the fel dot one. As for Seraphim vs FV, FV is clear winner for me with the amount of cleave/AoE you need to do on pretty much every single fight in HFC.
If ecounter/tactics allows it, what do you think about lining up 2nd ES with 4p, do you think is it worth the wait for extra ES damage plus potential RPPM trinket proc at the same time with 2nd AW up?