My 2 cents ... it's difficult to properly jelq at 100% unless using a mechanical aid. The shaft is too hard and too engorged.
What's called slow squash jelqs (if I'm getting their meaning right) can be done -- very very carefully -- at or near 100%. I'd always called them 'erect bends'.
And for normal-ish jelquing performed at 100% one can use a backwards-held canning jar lifter, or custom (small) 'rolling pins' to provide a material, shape, and mechanical advantage of leverage capable of deforming a shaft engorged to 100%.
++ Kal-el, ... be careful. Going at 100% takes some getting used to, for both adaptation and for technique.
.