It could be U shaped and not just a flat panel. Also, I assume the ceramic tiles have a very low coefficient of friction, so if it was stuck at any kind of small angle, the sediment might easily get carried off.
I got to hold a sample of one of the white tiles a long time ago. I don't know if it was identical to the flown versions, but it was anything but smooth.
I remember being able to feel and see individual silica fibers. It was very much a 3d surface.
I believe they are rather similar to the fire tiles you can get to line the inside of a blacksmith's furnace. They are quite light, but also very fragile.
I remember being able to feel and see individual silica fibers. It was very much a 3d surface.