If the Decathalon POH really does require "flying as PIC from the front" then how would an instructor sit in the back to teach a student in the front? I suspect that it will say that the aeroplane is to be flown "solo" from the front seat only. This is likely due to weight and balance or to the fact that some controls can not be reached from the back seat. Flying solo is different from flying with two people in the aeroplane and the Pilot in Command in the "wrong" seat.
Happy landings
3 Pont
PS I just found a Decathalon POH on-line; it says "Solo from the front seat only"