I'm tiling my washbasin top with 40cm x 40cm natural slate. The width of the tabletop is 40cm, and I have built a 20cm high pelmet which I'm also tiling. My sinks are about 18cm high and the taps about 26cm high. I was thinkng about tiling the splashback about 20cm high so it is the same as the pelmet. Is there a rule of thumb about this height? Or do you think 20cm is about right??