Slap bass is much harder to play on the D and G strings comparative to the E and A strings. It is also harder to slap on the frets above the 7th or 9th and get decent sound as compared with open strings up to the 7th/9th fret area.
You’re working with two real serious challenges simultaneously. I don’t approach these strings with lots of thumb action with my students until they’ve gone through a month or two of E and A slap, D and G pops.
It’s a tough place to develop technique, is what I’m saying.
Go back to open E and A, and if you get perfect sound there, go to open D and G until you get perfect thumb sound on all 4.
Then work on 3rd-5th-7th fret ideas across all 4 until you feel like you can keep solid perfect slap tone across all 4 strings fretted in the sweet spot of the neck.
Once you’ve got that, move up to the 10th-12th frets and see if it’s any better.