The wing span has nothing to do with the CG. You can however do a couple simple flight tests to see if the CG that you are currently flying with is ideal or not. First though you need to measure the airplane to see where your engine thrust line, wing incidence and stab incidence are. Then take note on where your elevator trim is. With an engine thrust at zero up or down, a wing incidence at .5 degrees positive and a stab incidence of zero, you should require no elevator trim. If you have up elevator trim with everything else as described then the odds are that you can remove some of that weight. Another test I like to do in an inverted 45 degree climb. Once established take note what the airplane does hands off. A proper CG will be a subtle arc towards the canopy to level inverted fligh that should take about 5 seconds. A slightly aft CG will have the airplane hold the 45 degree downline or even steepen the climb. However the first step to getting any airplane correctly flight trimmed is knowing what you are starting with.