Fuuucckkk!
Was just going to scroll and maybe post a quick salty snark....
....Okay super quick cause I love this question.
Rule of thumb you can't be hip thrown if your hip is in front of your partner's in the way I think you're describing. I'm in a hurry so I didn't read all the posts....
He's using his hip as the fulcrum to control your center mass, lift and pivot your body?
There's a great basic tutorial on Steve Scott's channel that visually breaks down the principles I mentioned.
Also the "angle"-I know there is a whole thread 'does Judo have angles' or something like that-the angle his or your inside leg hip and center are to each other. I think
@Zankou talked about grips, your grips are how you're angling your inside hip to be defensive, but positioned to instantly become offensive. The over hand or over the shoulder grip is your inside leg/hip power grip, your outside grip is to keep his balance unstable on his toes. This is really basics so you can start to analyze his attack and see that he's setting you up a while before you go "what the..." SPLAT!
I think the simplest way to look at it is you want to be generally facing the same direction with your hip in front of his, control of his body with your inside grip-there's tons of places to grip- control of his balance and mobility with your outside grip inside his sleeve grip-forgot to mention that, super important and makes it much easier.
When you're just gripping up that's your end game, that's the standing hierarchy of progress you're trying to achieve.
The kicker, and this is why I love stand up is you can instantly create that ideal throwing condition by your explosive movement or exploiting your partners movements trying to gain his advantage.
Stick to the simple ideas first till you feel them. So now it will be "what the...." "oh that's how he gripped" "dammit I felt that hip sneak in there too late" SPLAT! And eventually get to "what the...oh no you don't" "holy shit I'm still on my feet!"
Oh last but not least, when ever someone I'm training with gets the drop on me on a consistent basis. My god given obligation is to pester that person to train and teach me WTF they're doing. That's how you guys learn. He learns how to communicate technical ideas so if he ever teaches he's already done it, you learn how not to go SPLAT and learn a new strategy and chain of technique to a successful throw.
My best training buddies are probably, now thinking about, it all people who use to kick my ass on a regular basis.
Oh Jimmy Pedro who passed his grip strategy to Travis Stevens and all the players at the club are a good place to up your IQ with. I'm not sure if Travis has any tutorials, but I know that Jimmy has a few.
Crap, sun's coming up gotta train!