Secret to Better Flip Turns

I've always thought I had a pretty good flip turn and yesterday I got confirmation, almost. A former NCAA swim team coach was doing a favor for the guy in the lane next to me, evaluating the guy's stroke, when I stopped at the wall. Standing high above me on the pool deck, the coach said, "You've got a good flip turn there". I thanked him. Then he said, "You could do better with it if you just tightened up more on your kick-off". Not knowing exactly what he meant, I asked, "Tighten what up?" And he put his arms out front of him, grabbed his two hands together in a fist and forced his arms out dead straight. Relaxing, he said, "Your elbows are relaxed. You have a kink in your elbows". I tried what he suggested and instantly added almost two meters to my push off distance. I guess my elbows were impeding the slipstream.