Your plane isn't a world models ultimate... The two are very similar in size. That being said, the placement of the CGs should be very similar. So, if the World Models ultimate has a cg of 3.2" from the leading edge of the top wing (in the center of the wing), it stands to reason the the CG of your biplane would be in a close spot. Or you can set your CG out to 100mm from the LE of the top wing as opjose stated his was at.