Janda Situps

"Janda situps" are supposed to be an excellent exercise, and super-hard. Lots of folks say you shouldn't be surprised if you can't even do one. They work by taking your hip flexors out of the equation via reciprocal inhibition (i.e. you tense the glutes and hamstrings and your hip flexors automatically relax). There are lots of Janda situp descriptions out there, and the evil Russian even sells a $150 machine so you can do them unassisted.

Of coursre, I figured, "who needs a machine?" So I anchored one of my Iron Woody bands, put my legs through it, and slid back until the thing was pulling mightily on my calves. I had my legs at 90 degrees, feet flat on the floor, and the band pulling hard enough that I had to resist pretty strongly to keep my legs in place. I did the situps, and didn't have too much trouble doing 4 sets of 10. I mean, 10 isn't a lot of situps, but based on descriptions I figure I'm either [A] Superman, or [B] doing them wrong. Given I still haven't mastered the flag, the standing rollout, or the front lever, I think we can rule out [A] (I'd like to cut myself some slack because I'm 6'4", but really I'm only in the ballpark of the flag, and I'm nowhere close to the rollout or the front lever).

Anyway, anybody have pointers for me? Perhaps I need to anchor the band higher such that it's also trying to pull my calves off the ground in addition to pulling them away from my butt?