Contribution confusion

So, now that I'm all grown up (yay tier 2), I'm trying to get a handle on how this whole contribution system works. Specifically I mean PQs, as that's all I've had to deal with really.

So here's my data. All the PQs I've completed in a group:

Destruction of the weak (ch.2 norsca)
who: Czarnal, level 6 or so, and Tanith level 24 DOK.
contribution ranking: czarnal, tanith.

Ruinous powers: ch.1 norsca.
who: Czarnal, level 6 or so, and Tanith level 24 DOK.
First place: czarnal, tanith.

Macabre Fervor, ch.3 nordland
who: Czarnal, a lot of other folk.
contribution ranking: czarnal, everybody else.

Pillage and Plunder: ch.3 nordland
who: Czarnal, Magus, squig herder
contribution ranking: czarnal first, dont recall others.

Pillage and Plunder, ch.3 nordland
who: Czarnal, Bellagoth (11 WE), Mortien (10 Zlt).
contribution ranking: bellagoth, czarnal, Mortien.


Pillage and Plunder, ch.3 nordland
who: Czarnal, Derruba (7 BO), Mortien, Bellagoth.
contribution ranking: Derruba, Bellagoth and Mortien, Czarnal.


Fields of Woe, ch. 4 nordland
who: Czarnal (11), Derruba, Mortien (11 Zlt), DaveJones (11 Mrdr)
contribution ranking: DaveJones, Derruba, Czarnal, Mortien.

These are contribution rankings, not rolls or loot order. So it's not perfect data, small sample sizes and all, but a couple oddities have struck me:

1. how the crap did I out-contribute Tanith twice? full disclosure, in addition to being a third her level, I also spent most of the PQs scavenging.

2. healers aren't getting enough love. Fields of Woe ... no disrespect to DaveJones who dished out the hurt, but we could have completed it without him, in fact we had on a previous attempt wiped only because we stood in the road where all the champions rush out and fought them all at once. When we respawned we killed them all, just ran out of time. My belabored point is that without Mortien we have zero chance of completing. Everyone else in that setup is expendable.

3. I wonder if contribution is distributed by role. Maybe this has been discovered, released, explained and I've just missed it, but for a tank to win, it can't be damage / healing numbers, it has to be some tanking calculation: damage taken, time that mob has tank targetted, damage mitigated, etc.

so, does that hurt hybrid types? healers that are DPS specced? DPSing tanks?

4. splitting the responsibility hurts your contribution score. This makes sense to me. Two tanks means each is individually less vital. So we score lower. One dps class? bigger contribution. I would say that given the relative roundness of classes (tanks and healers can also do decent damage, not one-dimensional), dps is probably less vital in and of itself. Now if they kick the ass, well then nevermind.