It's a tough problem. I've had a somewhat regular stream of requests for this. I've always been concerned that the floor level would have to be higher than other tiles. Maybe I could at 2-4 mm to them to get just a little more room in the sluice, but honestly this solution looks pretty tight. Or maybe what I could consider is adding a stone border around the sluice so that it's edges can go above floor level.
Anyway, great work, this has been vexing me for literally years at this point.