About the ten tefach mechitza ( I have seen mamy, the lucite, the walnut, and the lucite side by side ) add this to the cheshbon; a mishna in Eruvin, that a roof adjacent to reshus harabim that is ten tefachim high, the public is oser on the baal habayis use of the roof, because the public will off shoulder their loads onto it, meaning that for the mishnaic everyman, shoulder height is 10 tefachim. My terutz is that maybe people in that time were really short, and with big hands.