In that above Ono video, he reaps and looks "through" the throw, as in underneath and behind him, which seems to facilitate the roll-through.
I did that the other day for my speed drilling, and I liked it, but I don't know if that's what you were getting at or not.
The hard thing in Osoto Gari is to get into that offset position against a resisting opponent, same as to get into the "t'ed up" position for forward throws.
I've found that how and where exactly I step or move depends greatly on relative size of myself to uke, weight, height, gripping situation, and all that (in order to get uke at enough of a disadvantage to attempt the throw. So how exactly I use my sleeve hand and head control varies quite a bit.
The "generic" cross-body Osoto Gari gets around some of that by pinning uke down with the hooking leg and then adapting from there to what/how uke reacts. Still requires the other elements, but the whole need to get offset tends to be diminished.
A lot of O sotos fail because people drop their head too early and lose power. If you watch the Ono video you'll see as he engages and gains chest contact his back is totally straight regardless of where he's looking.
The best analogy I can think of, which probably won't mean much to an American is scrummaging. The way as a front row forward you need to be able to crouch whilst maintaining a straight back and good body posture.
An example, look at the straight back and excellent posture well into the heart of the attack, uke is already critically off balanced and on his way to being thrown.
It's only once uke is thrown that he starts to really look towards the mat to aid with the drive to completion.
When I'm coaching people on Osoto I tend to tell them to attack from the hips, not the shoulders, this doesn't mean literally hip thrust towards them, obviously. However, I do it to try and get them to consciously not lead with the head, which achieves the real aim of them leading with their chest.
Be interesting to see some video like in the Uchi mata thread if you're up for it.
For me the cross body O soto generally blows the whole offset mechanic out of the water. Once you're in that kenka yotsu position with sleeve end and lapel control then the offsetting thing goes out of the window. However, not so, in my experience, if you have double lapel or lapel and armpit from the kenka yotsu, then you need to do a cross body O soto like Pedro demonstrates where you come in diagonally, but then hop/drive into the canonical offset position.
Rotate shoulders and head (to finish), turn inside hip down (close the hip). This all facilitates contact and thus control of uke all the way to the ground. The same elements are in the standard throw with a standing finish, or if you drive into uke and into the ground without rolling through.
I also only slide/drive my leg down to their ankle if I'm attacking from kenka yotsu with double lapel and or lapel and armpit, in which cases I hop/drive in and round until I'm chest to chest with uke.
That is a point I emphasize very very strongly when teaching. Head needs to be up, and the spine in as natural a position as possible so as to be able to maintain the widest range of motion.
Obviously, that doesn't always happen. In a sense, tori relative posture and position needs to be sufficiently better than uke to execute a throw. When dealing with skilled opponents, where the margin of error diminishes to practically nil, posture must be excellent to have any chance.
I've never slid down to the ankle, I should try it though. Osoto wasn't and isn't my go to throw, not that I have much in the way of that anymore, other than various ashi barai.
To avoid any confusion, please describe to me the ridge of the knee. The kneecap, the area related to the IT bands, hamstring tendon, or what exactly?
I know this may be unnecessarily specific, but I like perfection.
Make sense now? I had to look up the anatomical names LOL.
That tendon also makes a nice place to hook your toe(s) when doing Hiza Guruma.