The reason armory does not show that you have 17% Hit is because you got the Conclave belt, armory don't show the stats, and I guess you reforged that into hit
The reason you pull out low numbers could depend on many things.
Are you using scorch every time you move?
Do you run out of mana?
Do you maximize damage output on all available targets?
Some fights for instance have more than 1 target.
Valiona & Theralion, you can deeps the one thats flying above, keep living bomb up on both, if you get lucky with hot streaks and get 2 fairly close to each other throw the other pyro at the one in the air to get a dot + possible ignite etc. then go back to nuke the one on the ground.
Cho'gall, while dpsing the big adds you can keep living bomb etc. up on Cho'gall, and if your guild are pulling the boss to throne or w/e in last phase so the tentacle eyes are bunched up you could get some nasty numbers getting a combustion + impact on them as soon as they spawn.
Nefarian, keep living bomb on both nef and ony in p1, if your guild nuke for a crackle in p2 your free to dps Nef in the air while nuking the add on your platform aswell.
I just used above fights as examples, I'm sure you can figure out other fights where you can do similar things.