Just echoing some advice given, as PLD OT, the most successful runs on specifically P6 have been when everyone but MT group dead center, as insurance only I've popped cover on the WHM in the group and after a couple of seconds, I'm flashing and use CoS to get all aggro. I'm usually slightly south of center, far enough away where bugs won't get gobbled, but close enough to group so flash and CoS hits everything. Pop HG, then hold somewhere south, running circles around the mobs. The two things that have always made it go wrong: a healer or both are away from or in completely different locations from me and each other or DPS starts going pew-pew without even waiting two seconds on an add.

As PLD doing OT, it seems far less chaotic to just group center for P6 adds, grab and move away, then people in different locations, hoping I can grab and keep aggro on everything. Especially since the healer will have already started healing.