I'll confess I watched you doing Uchi Mata and then skipped ahead to the end of the video, but there is something on Uchi Mata I want to pick up on, because a mistake you were making is very common, all the way up to black belt level and is a pet peeve of mine.
Correct body positioning for Uchi mata is almost exactly the same as that of Tsurikomi goshi,
For this reason I advise everyone trying to develop their Uchi mata to spend some time working on that throw first and then returning to Uchi mata once some basic proficiency is achieved.
The central issue to ensuring correct body positioning is making chest contact and maintaining chest contact between tori and uke throughout the technique.
In order to ensure this chest contact head positioning must be correct.
Head drop is the killer here.
The main error in head positioning for Uchi mata, which directly causes the main error in body positioning i.e lack of chest contact. Is that people collapse their head when trying to complete the technique.
This is what you're doing, bending over at the waist and basically just dropping your head.
Bent over at the waist, looking down at the floor and with their hands trailing behind their head.
From this position you have not only lost control of uke, but are unable to apply any power.
To ensure correct head positioning rotate your head through a rough 90 degree arc in the direction of the side of your body off of which uke will be thrown.
In addition to not collapsing your head and keeping it in the correct arc. It is also important not to over rotate the head.
Often in Judo we’re told to look where we throw, bizarrely this always seems to translate into people turning and looking over their shoulder in exactly the opposite place to where their uke will be thrown into.
A simple test for whether you’re over rotating is which box do you finish the throw looking in red or blue
If you said blue, you’re over rotating.
So, remember one and all, when doing Uchi Mata ensure chest contact, throw by rotating and not by dropping your head and bending over at the waist.