It relates to the height of the shower head relative to the cold water storage tank I thought, everything else inbetween is irrelevant.
So the cylinder/water tank is actually in a single storey flat roof holiday flat. The water tank that supplies the hot water cylinder is situated above the cylinder. The gap between the bottom of the water tank to the top of the hot water cylinder is probably only about 12 inches.
https://www.google.co.uk/search?q=p...wKHV0KC20Q9QEwAHoECAQQAw#imgrc=m12P-oERs4YnMM: This should help you understand the difference.