That's why.

In addition, the original poster put this question out in March. Most likely, he long ago decided what to do, and our comments now are moot to him. In my March 10 post, I merely told the orig. post author how mine was built (on the advice of our club's instructors). Adding the power of a light .40 had no ill effects on the flying characteristics of my plane, so why not? I had the .40 on hand, a .25 I did not. The weight difference between the Fox .40 and the OS .25 FP I had is only about 2 ounces. Turns out I needed to move radio weight forward even with the .40. So, not net weight gain, as I would've needed about 2 oz. of ballast anyway.