The thing is that these techniques I used on the Judo student were done after asking him to attack me with an overhead strike and a punch to the stomach, I knew what was coming, I doubt I would have had as much success if it were more like randori.
When he attacks, he has the initiative of engagement- that is, you must move to counter his attack. If you do not move
This means that he is in control- so you must try to take that control from
him. The priority is taking the initiative away so that HE
is on the backfoot. If you move in behind him (i.E tenkan behind them) You can take the initiative by pulling him to the ground or striking at him- Now HE has to move to counter you and so you can dictate the battle.
See how it works? When you do a technique, what you are actually doing is taking the initiative away from the opponent as you are throwing them and they cannot attack you- they have to counter or respond by taking Ukemi. If they break out of the technique and you have to move- they retake the initiative.
However, if you just back off the you have a face off. The first to attack successfully will take the initiative of engagement and the whole damm thing starts over again.
You don't have time for this so the key is to figure out what attack he is going to make as they do it. Others on other threads believe that you can....
"pe-empt this attack before they make it, while they are squaring up or getting into posture"
Nonsense. If you move before the attack, they will simply change to your new position or change the attack. (we do it at home all the time).
One must wait for that split second to see what they are doing- until they are committed- until the last moment to move before you do to see what is coming. Once they are committed the cannot abort the attack (the blow is already coming your way).
Now you know what attack they are throwing and thusly can counter it on how it falls. This kind of reaction only comes with experience however and takes time to develop. good luck with it and keep up the hard work.