Thanks! I guess I should have emphasized that as a major relationship instead of sounding like something more unique to stiff vaulting...
Although my point is still quite valid. If you don't have a high plant and take-off on a stiff pole, you'll feel it...especially at a reasonable grip height...and I mean you'll really feel it... Stiff poling REQUIRES this, but when you're on a pole that bends, especially a pole with a high flex and is right at your weight, you can hide these problems for a long time. Me, I've just begun to all drills with a stiff pole, even vaulted in a meet with one. It's sort of like a detox for the ineffecient vaulter.
My advice is to get on the biggest pole you have access to and use it in practice for a week or two, running with it, sand drills, actual jumps, plant drills, etc. This will give you a feel for the need to do everything as perfect as you can as often as you can, especially when vaulting into the sand. Also, I would believe that taking a couple trotting plants into the box with a 15 footer and just popping off the ground a little will help give you a psychological edge on moving your grip up. Hope that helps!