What ronk 1 suggested is a good idea. The reason most designers plan for balancing with an empty tank is at the end of a flight the CG will be somewhat near what he (the designer) planed to be optimum when landing but of course there is nothing wrong with landing early in the flight.

The CG is constantly moving backwards during any flight and the further back it moves the more pitch sensitive the airplane becomes complicating the landing difficulties.

John