it can be smooth and still clean- it can also be sticky- so can a 3. You're assuming these poops arent sticky because the chart doesnt say so.
It's the 1-2 and 5-7 that are the problem-
1: Shotgun effect- splashback all over your ass
2: Too rough, hello Hemorrhoids
5: Splurting out your butt and doing splash damage
6: Enough of this and you create a small mountain of poop that could potentially touch your butt
7: With enough force you're doing splash damage again
