Vince

Of course I do know the Phoenix , only the rule of thump I will never advice.
A first flight is never a situation of trial and error, so why take risks? Why adjust a stab on 0,3 degrees and accept deviations in calculated cg position?
My advice, if you want a fast check, mark the wingtips with the original CG position and you can use it to do a fast check by balancing the plane.
I have these points on the centre section (bottom) of the plane.
See picture,

Cees