You are correct about the stab relative to the centerline that is exactly where it should be. I empathize with your dilemma being a designer and a scratch builder I have been there more than once. I have Dave Platts' plans for and exact 1/6th scale Se5 and he shows CG to be 2.7 cm back of the top wing leading edge. My intuition tells me that this too far back but in reality I do not know for certain. With all the Scale Se5s that are flying go with what these knowledgeable modelers recommended for they truly must know for certain and base this on reality not theory or math. It is also correct that the nose should be at a slight nose down attitude. I would be very interested to know where it ends up as someday I plan on building the Se5 kit that is tucked away in storage. Good Luck !