Well you can answer that question yourself easily by turning the plane upside down and using the same CG measured points (3.5" from the leading edge but don't change what you have already done to see the difference). I think you'll find that it no longer balances out.
The old field geezers are CORRECT with their recommendations, I had to balance every Mach II our club has put together in the upside down position to get rid of all the extra weight needed compared to rightside up. Matter of fact, we're running o.s. .46 engines and most are balancing out real nice by just moving the battery pack around. I'm running a ringed o.s. 50 on mine and it's scary fast, no added lead to get good CG either when balanced upside down and the planes fly great.
8.5 oz. of lead is way to much in my opinion for such a lite weight plane.
Good luck