Gary,

The directions state and show four washers on each side under the back of the mount. Though I haven't flown the composite Roo yet, this seems excessive. Most of us with the original Roos ended up with 1/6" under the back of the engine. Andy was also correct about the 1/8" reflex. I do recommend that you put different rates on the ailerons as 20 mm provides a high roll rate. Have fun today.