Matt, you aren't alone, and I don't even know what a Ml is but if he's talking about a 16 ounce tank, I'd say fill that baby up! Even if it's behind CG, you have it as your last tank, and your airplane will be well balanced for takeoff, and become more nose heavy as the flight goes on, and then come back go CG for landing. I have done this with great success (so long as you are truly counterbalancing against the fuel ahead of CG)