As described, the Defender has engine problems. The mass allocated to Acceleration is more than enough to give the craft an acceleration of 3. This introduces an upgraded-engine model (also described in the book), with it's full acceleration potential realized.
There is also a Red Fox Industries version of the Defender. Personally, I think the rear fuselage of the Defender should have no armor at all; just look at that tail mount. And take a look at those wings, they are huge. Thus, I have moved some armor from the back of the fuselage to the front of the wings, and added the extra armor to the wings as well. This gives the defender more wing than fuselage armor.