As an amateur player I don't have sleepless nights worrying if my MPC table should be flat or concave. 
However, when faced with the question of whether to flatten a concave table or not, I usually do so. This is purely based on the feeling that a reed which is swollen into a 'U' bend, possibly all the way to the tip, cannot vibrate as well as a flat reed.
This poses the question :-
                           Should a concave table be extended all the way up to the end of the window, or given a flattened section just below the end of the window, to improve the seal at this point.
This would split underside reed swelling into two parts and stop saliva being forced on to the table directly and then only by osmosis which will delay the swelling in the concavity area.
A flat table of course eliminates all of these problems.
EDDIE