I can vouch for what the OP is talking about - I've had a few guests smoke the way he is describing, and it always seems to kill the session. I'd concur that they aren't moving enough heat/air through
the shisha, allowing it to burn.
I'd suggest talking to him and explaining what his technique does what it does to the shisha and the session. If you just say "Dude, take bigger pulls or you'll screw up the shisha" that won't work. You've got explain the WHY it does what it does, so that he understands - once he does, I'm sure he'll change his habits