Ah, that looks more Hornwortish. My mistake.
Can you redirect the flow of the water off the wheels with a baffle or something? Perhaps its a matter of two causes, both the draw of the intake and the push of the flow. I mean, normally we'd want that. But maybe not in your case? Would it help to create some secure barrier (wood, rock, other plants) between the Hornwort and the intake that would buffer the pull of the intake? I don't know.
A thought I've been tossing about in my head is of somehow finding or concocting a device to anchor the plant in one spot. I don't like the idea of lead plant weights. So another idea would be a geegee that is shaped like a U hairpin, but made of plastic. I was thinking that I could then put a stem of the Hornwort in the crook of the U and insert the free ends into the substrate. It would still be a loose bunch, but would be loosely connected to the substrate in one spot. Do you know those plastic clips that come on new socks, not the miniature hangers, but the ones that are like plastic bobby pins that hold the toes of the socks together? Sometimes they come on packaged men's undershirts, too. Those might work. Or maybe a fishing weight (careful to make sure its aquarium safe) tied to the Hornwort loosely with fishing line, and then burying the weight in the substrate? I've even considered using a zip tie that is looped loosely, then siliconing it to a small piece of slate, then burying the slate so just the top bit of the zip tie loop is above the substrate.
So basically, those are my ideas. Maybe one will help? Or else, I hope someone has some better ideas! I'll keep an eye here, because my Hornwort and I also disagree on where exactly it should reside.