Rich the reason it flew like it did when you flew it is you surmised correctly the CG is typically further back in those kinds of airplane and there will be a distinct demarcation in the change from flying on the wing or prop hanging. It may be back as much as 33%.

For more fun with that airplane especially if you just want to fly it is to try it at 25%, it will fly much nicer for you. To acheve 25 just measure the average cord and divide by four to make that you target distance aft of the leading edge. Actually I did that just mentally by looking at one of your photos and it appears the 25% is right at the rear edge of the spar.

John