Yep. Its because you are new to judo.
All due respect, the typical wrestlers crouch is the last thing any would want to do in a gi with grips on each other.
Are you specifically talking about a wrestler or just a bent over fighter?
You would have to be more specific but I'll tell you, as you said you are new, the answer is in the basics that you have prolly been learning.
I would really just keep trying harder to make what you have learnt work.
crouched fighter? Maybe since your new and lanky try osotos

and a taiotoshi/koshiguruma thing(head and arm but with a behind the neck collar grip). Just take strong hand grips with a flexible arm, body and legs supporting them and attack often taking risks and forcing the throw sometimes. Twist him, wring him and smash him and keep attacking with it while controlling with your grips. One time it'll score, it'll click in and you'll know better what your looking for.
Its important that you really learn to get comfy with just moving around and staying in control with your grips on the fighter.
I bet I can tell you half the mistake right off the bat, especially if he is a wrestler. He's goin hard and you might not have 'learned' how to yet.
Wrestlers 'take it easy' at practice and thats still goin 95%. You as a typical judoka working with other recs who wanna take it easy(doesn't happen in wrestling) might often have to work your osoto like 'twist, leg behind and drive all while smoothly accelerating torque to maybe 100%' and that sucks. When you fight another 'vet' be it judo or wrestler at judo, you gotta smash him. You can save power for certain times but when you work shit in randori you gotta be split speeed and IMPACT baby! Don't fuck around thinking lets see how this works. Just sssssss...BAM! If it didn't work, then make sure he at least felt very uncomfortable in your attempt. Its an offensive sport. Take lots of risks and beat him down in the process. Lots of light, explosive uchikomi and lots of heavy randori.
See my av to the top left? Power kill machines. These fellas would make sure that the tech they have REALLY didn't work before moving on to another. I bet.