Hard to explain for me, even though I sort-of know the answers.
The way rampjumping works is, it basically adds "positive z velocity" at the cost of x/y. There are ways to lose less speed, but also gain less height. You can hit the ramp at an angle instead of dead-on. I was actually wondering this yesterday, but I think that if you rampjump within 400ms (first half; basically a doublejump) of the first jump, you lose less speed and go substantially higher, because it adds the velocity from a regular doublejump to the rampjump. If you hit the ramp while falling, you'll lose a lot more speed and gain a lot less height. Hitting ramps earlier in the jump is generally what you want, unless you've got some weird route that requires a really low rampjump.
I'm pretty sure that's right, but I don't know if it's even an answer to your question.
Doublejumps just give you + a bunch of velocity. No matter what, you'll jump 91u (a normal doublejump with nothing else interfering; you can go a bunch higher under certain circumstances).
I don't know much about air control though. I can use it, but I can't explain it. That's how basic my understanding of it is. It's a beautiful thing, though. Climbing walls is fun
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I expect someone who knows what they're talking about to come in here and destroy my post with their uber nerd-level knowledge.