The Gemmorah (Succah 3 and Mishna on 28) states that the requirements for a Succah are that a person can fit it "ראשו ורובו" - the head and most of the body.
IIRC the average body is 3 Amot (18 Tfochim)Gemorrah elsewhere and the head is about half Ama (3 Tfochim) for a total of 21 Tfochim (5'9 or 175cm). So, Rosho (3 Tf.) + most of his body (10 Tf) would equal 13 Tfochim.
We know that they ate laying horizontally on beds, otherwise, if one sits or stands vertically, IMHO, Rosho AND Rubo is meaningless, as the head is above the body.
The Halachah ruled is 7x7 Tfochim.
I see a contradiction here, how can it be reconciled?