Payload Range Diagram

After my last post a debate started about the range of the B737MAX-8 and -9, precisely whether these ranges can only be achieved with an additional fuel tank. It seems like (and Scott Hamilton pointed us to that) that Boeing already said that the MAX-9 range of 3595nm is reached with an additional fuel tank. Boeing did not say anything about the MAX-8 fuel tank configuration to reach 3640nm of range, but it seems logical that this will also be only achievable with the additional fuel tank.
A further hint to that is the difference between the different OEW and MTOW gains, relative to the NG.