I dig it.
It reminds me of passages in Kimura's autobiography.
He discusses O Soto Gari repeatedly.
He discusses opponents defending, but he insisting.
He discusses the transition to O Soto o toshi where the foot plants and straightening of the leg lifts uki's leg and furthermore the transition from that back to O Soto Gari.
There is a magic between the moment to moment differences of the attack with hooking near the knee to bend it, planting and straightening your leg with a forward drive to overcome a stiff heavy leg, and full upward airborne reaping motion of your attacking leg.
The armpit grip is interesting. I enjoy the nogi version of tricep control off a clinch or if deep enough underhook gripping your hand coming over the opposite shoulder (head and arm control from clinch).