Your P1 sounds about where my guild was when we were progressing back in Oct/Nov which is fine damage in P1. The only important part is that you don't hit the 3rd Eng.
(Note that my guild still occasionally fails on this transition. It's really difficult depending on 10m comp and what classes you have)
I have very similar gear to yours and with an opening CB + 1 conflag on each mob they're usually very close to 20%. I'm with our BrM tank who does about 50% damage to the third add and the first 2 groups + me finish off the third add. Note that this is without procs. With procs it's likely that I won't have to Conflag so I'll conflag the 3rd add instead. Remeber to glyph CoE and apply it to the mobs. Note that I'll typically try and hit 3 embers during the ICD on 4pc as we fly up to the zone, and then let the 4pc proc off of the 2 RoFs on first two groups at 4 embers.
All 3 adds start their engagement the first time one of them takes damage. They'll melee and then cast every once in a while. I don't think you have to have someone in melee since they can't move.
I used AD to consistently get down Engs every time, which means I get 1 charge of DS right when PBoI procs during the smash phase in P1. The timing works out pretty well there.
You can watch one of our kills from my PoV as a VoD on my stream: http://www.twitch.tv/brusalkstream/b/500851471 @ 4:08:00. I knew my 4pc timing was going to be off so I bled an ember before transition to buy time so that my RoFs would make me hit 3 embers rather than 4. There's a lot of other stuff I do on that kill which I could talk about, but there's a lot. :P
EDIT: Looking at the VoD looks like a probably cast an Incinerate or two that I'm forgetting about on the higher health one of my 2 to hit 20. I'd def say don't run with havoc glyph depending on P2 weapon strats. You lose a Havoc every 2.5 minutes running the glyph.