That's been discussed on a few Trek specific boards and the conclusion before the HD caps was P1's on the left and P2 power packs on the right hand. I think the HD caps prove this... the closeup I posted shows midplates on the P1's on the left. The midplates don't normally go around the back of the P1's but there have been enough screen caps of midgrade/craps of P1's that showed the midplates painted all the way around the back of the phaser.