If it is touching a wet floor, it doesn't matter whether it is top or bottom does it?
I mean, touching the wet floor is what makes it wet, not the direction
No, I think it does matter. If the paper is coming off the top, it's very easy to fold it over as you are unrolling more. If it's coming from the back, along the wall, it is more difficult to keep a long piece from touching the floor. The tendency is, once you've found the end, to keep pulling more from near the roll, not by holding on to the end.
They make miniature, upside-down showers for your posterior, you realize? It squirts a little, ice-cold splash of water on you when you're all done. Works like a marvel.
Over the top <--- how I install it
Under from bottom <--- I don't mind if somebody else always does it this way
Who cares? <--- it drives me crazy if people are inconsistent about it!