i am sooo terrible at this technique (and well, most others too) but i can say what i think from an uke view point. it seems a bit more effective on me when nage is not thinking about moving me down, as much as moving me around and in (close to nage) with a touch of down, then just at the throw a little down, up, and down. i think that approach might also work better with the giant ukes, who i also think need to know to lower their center rather than bend over at the waist (which is begging for kaiten nage in my book). But just grabbing the head/neck/other body part on me when i'm uke, and pushing down seems to just 'pin' me to the mat, stopping me from moving---of course, i'm usually a lot lighter than my nage.
i think of it like a satellite being pulled into a planet's orbit, swung around, and 'sling shot' out the other side, with the little down-up-down at the end to direct the relased energy. anyway, it feels better to me, but i am a beginner....