I would think the long curve might be subject to harmonics as the wave passes through. Constant changing of the angle as the wave reflects off the pipe. I may have this all wrong, but I have this visual of waves bouncing all over the pipe in the curve.
I tried a Kanstul 1500A and found I had to put a little more behind it than my old "D" slide. It was stuffy before I pushed it and really lit up after I did. More resistance at low density? But there were a bunch more variables than just radius in this case.