Oh yeah, concentration is a huge factor in smoking crack. Thick smoke (vapor) is necessary for the most intense hits. That's the main reason you can't do it nearly as well on foil or hot-knifing as you can using a glass pipe -- the strongest hits are thick like milkshakes. And, if you get much air in your hit, you won't get the same rush. You'll actually get a more intense hit if you stop as soon as the vapor in the pipe starts to thin out than if you keep heating and pulling the hit -- you'll consume more total vapor, but proportionately more air. I don't know the physiological details, just the practical technique. A really thick hit of crack vapor from a narrow, glass pipe is the strongest -- and also the most dangerous. I'm not sure if it was a stroke (the docs ran CT scans on my brain a buncha times), but I had something like that with a "perfect" hit once. Like breathing in a lungful of creamy crack sauce -- then *poof* I'm on the ground, almost paralyzed, no idea where I am, who I am, what's happening.... Several days in the hospital, couldn't really walk very well at first actually.
P.s. that was a couple years ago, and I pretty much quit after that. Can't remember last time I smoked, snorted, or slammed coke.