Those always came naturally switch to me, and so does it seem to for a lot of people, I think it's because on those the movement is so similar to regular ollies when you're in the air it's generally more instinctive to form. I kind of forever had the same problem as you which is decent ollie height with a nosedive yet bad form on the feet, then eventually learning crooked bonks and doing more nosebonks on and over tall-ish stuff (for me) somehow had the side effect of helping me get the timing and motion right, and now it's not uncommon that if I'm going to do a high ollie I'm going to think of it as a nosebonk that's going over and past the obstacle (if there even is an obstacle outside my imagination) as opposed to, well, bonking it. Not sure that will help but doing those tricks a lot might do the same for you. I still have pretty shitty form on regular ollies to be honest (compared to how I'd like them to look), but it's a lot better than it used to be.