The P1 seat on the L4 is the rear seat and it was designed that way. Simlarly the Supercub was designed/adapted to be flown P1 from the front seat. If nothing else I would be concerned about the insurance position if something went wrong with a non-qualified/qualifying person sitting in the P1 seat.
The instruments can be a bit difficult to see with a large front seat pax - you just have to ask them to lean/tilt their head to one side - otherwise I don't find much of a problem