After several hours of testing at a dummy and in Firelands, I have come up with a way to nearly double the strenth of ignite. I will refer to this as Ignite Stacking. Similar to Ignite Munching, but with the opposite effect.
What is ignite stacking?
Ignite stacks when a target is crit twice (or more via Dragonwrath) before ignite ticks (2 seconds) the ignite's strenth will stack and be nearly twice as strong. Two hits at the same time do not (from my observation) cause ignite to stack.
The idea here is hold onto a Hot Streak Proc until a Fireball Crits, then cast the Pyroblast. Please note that you MUST be close to the boss for this to work. If it is a boss like Ragnaros the delay time is greater than 2 seconds and only by luck can this be obtained.
What if I don't believe this "Guromin" guy?
Try it for yourself! Go to a target dummy and cast fireball until it crits a few times and take note of the size of the Ignite from that crit. Do the same with Pyroblast. Afterwards attempt to obtain a stacking ignite by casting a normal rotation, holding Hot Streak until a fireball crits and unleashing it. If it crits, and the timing was good the ignite will be noticeably larger than anything obtainable otherwise. For me, I got about a 12k ignite from a normal Fireball crit and about a 14k ignite from a Pyroblast crit. With ignite stacking I was able to get anywhere from a 17-27k ignite.
Why does the value vary so much?
I don't know... My best guess is that the closer the two crits are together the more powerful the ignite is (but they can't hit at exactly the same time).
I can't get them to hit close enough together because of GCD lockout. Help!
Instead of chaining Fireballs, cast one and wait to see if it crits. The second you know it crit, cast Pyrobast. The second you see it hit, but not crit continue with another Fireball. If you keep chaining Fireballs. Don't ever waste a Hot Streak Proc! If the duration is under 3 seconds use it, don't lose it.
If you have questions feel free to post them. If you just want to leave a comment to say it helped please do so because it helps with my data collection. If it did not work, I'm eager to hear what caused problems or where I wasn't clear
-Guromin
P.S. 107th post. It took my guild 107 attempts to kill Heroic Rhyolith (one of my least favorite bosses).