Because it’s a curved in every direction. I would duplicate the wall so I can extend to make a cut out.
You can duplicate upwards into some memorable offset like 5mm so you can move it back down to the correct location easily.
Duped it and extended it 1mm, the hook will be 1mm in height, also I project the bottom of the rail down.
Using the projection, I figure I make almost 2mm wide hook, you can add smaller line to make total 2 mm in length if you need more precision.
I choose area that had the most curvature, just to show more extreme example.
You can extend that sketch to create a face you can use to draw the hook.
I used the bottom edge of the rail to project it on to the new face and sketch what looks like a hook.
Created the hook you just need to move it down 5mm.
and use the bottom face to project it down so you can make the cut out on the floor.
Hope that made sense.