The best starting point for CG on a biplane is as follows......27 to 30 % back from the leading edge of both wings.....make a little mark.......now draw an imaginary line between the two marks....the CG will be on that line at the middle point between both wings.....

Thats a starting point, as with all airplanes the true measure of CG will be in flight.....to test CG fly the airplane....go into a 45 deg climb and roll inverted.....let go of the sticks.....if she climbs she is tail heavy.....if she dives she is nose heavy......bare in mind your fuel load, as you set CG with an empty fuel tank so that when you fly you burn fuel off to CG....

Usually you don't notice fuel load too much.....what you will notice is that a tail heavy airplane is very difficult to fly....sensitive to pitch inputs, dragging her but around the sky if she can be controlled at all...a nose heavy airplane is a little more sneaky to detect.....you'll find that she doesn't want to slow down on final....and that you'll think you aren't flairing soon enough.

bottom line if you set CG and you like the way she handles your good to go....