How we scientifically arrived at this quantitative Fact, is pretty simple. As observed in the research history of the iWipe Innovation where the Study of the Human eye in Relation to the Human anus. Where it was discovered that these two organs are equally intelligent as far as the sensitivity is concerned. How that when you approach an eye for example with a finger it has an intelligence of its own that makes it shut without you shutting it; then if you approach it with a sharp knife or hot wire it'll shut at a much further distance. The underlining principle is that the more dangerous the object is the tighter the organ shuts; that's exactly how the bum also behaves. Now imagine how different objects have faired over centuries of human wiping evolution. From stones, grass, sand, leaves, paper, till dry toilet paper. Let's just say stones could only clean 5-9% etc.
Let's take it a step further and use yet this very simple example, to explain the same bum condition. If you pout your mouth like you are about to give a baby kiss with both lips together, we can figure this out real quick. Even easier if we imagine one who is putting on say a red lipstick on those pouted lips. Ok let's assume they start painting the bottom lip, from the bottom/lower edge to the top edge of the bottom lip; now that's 40%. From the top edge of the same bottom lip where red lipstick stops to where the bottom gum inside the mouth begins, that's 60%; meaning from the bottom gum to the lower edge of the bottom lip is 100%. The same angle/ length is true for the upper lip from its top edge to the beginning of the upper gum.