SJSinNYC:
Well said. Halacha is exact. “four inches” either has a Mekor, is made up, or is an approximation for something else that has a Mekor. Teen (or anyone) can ask for sources, and if not given them, ask/follow someone who will show sources.
(off topic, but a followup to a closed thread (please allow))
(SJS: As far as the Chachamim & reality, I tried and was blocked (correctly, I might add). Have a look at Dafnotes for 12/20/06 which brings the idea.)