For what it is worth, looking at the first photograph and if I were about to test fly it, I would want to bring the tail up a small bit and I would do just that. To my eye it doesn't look level but close. However I think it is highly likely that balance at the 9 cm point would be manageable as a starting point. The big question is was Dave Platt wrong? and the plans you have wrong? Maybe the CAD designer used Dave's design and carried the error forward? Who knows? It's either that or they are both wrong and I have to wonder how likely that would be.