Suwari waza actually are harder (or, at least, a bit more complicated ) to do than standing kokyu-nage waza if you are training the internal principles.
Just fwiw. I have a student that I've been working with for a while and going in to some of the IP stuff. When that student does suwariwaza, she realized she wasn't able to do the techniques as well in seiza as she was standing. She asked if she was doing something wrong and I just laughed. She's vastly more stable and able to do so much more than most of the others across the board. So when she found herself a bit restricted on the floor with her legs out of the equation, she noticed the difference. But from my perspective I just saw someone still doing vastly better than the rest of them. I was happy she noticed and explained to her that the difference was that she had become quite good in integrating her lower body in to her "unification of mind and body" skills. So the increased difficulty was really about the high level of her ability overall rather than a lack thereof. She wasn't having any problems doing the techniques in seiza. She just realized they aren't exactly the same if you're using more of your body in an integrated fashion and lose *some* access to part of it.
The experience kinda toppled a couple ideas I had long held but never really thought through. I like when that happens. Good to nuke old ideas now and again...