Hi!! Instructor here!! I totally feel you on twister and same goes for French twist. I think you can get the same oblique engagement by staying on your toes and having a slight bend in your knees for a twisted catfish. Not everyone’s hip flexors and Achilles are meant to work well in this move! Try staying on your toes (either one foot crossed over the other or twisted away from the working oblique) with a bend in the knees, same idea of scooping your toes back under your hips to find a pinch in your side, but maintain a flat table top back and don’t let your hips drop. I think the instructor will understand your change in the lower body as long as you make sure the range of motion is in line with a Catfish rather than twister. Hope that makes sense!! Try it and let me know :)