CH- you are making way too much work out of this .

hee is a very simple approach which puts you "close enough" as there is NO perfect CG --
I have th same model ,by the way with a 480 EFite motor and 1320TP batt and 11x5/5 prop (quick response setup)
Doi this
take full span - call it 40 " whatever - half that is 20 and half that is 10
measure in about 10"from each tip rib.
that point on each panel, wing is about the average width (chord) of the wing.
so treat is as the entire chord .
at that point measur back 30%
say the chord there is 9"--30% would be 2 and 3/4 inches.
-If you connect this point on each wing panel with a straight edge you will be able to magic marker a point on the fuselage.
with thumb n forfinger--pick up moder under this point
worrying aboutmaking cg adjustments upright or inverted is a waste of time - c/g is cg - do it easiest way for you.
now fly it - if you feel it is too stable - move the batt back some .
the trim charts will give you something to do - but basically with the model done straight and hinged decently - it flies extremely well -- forget thrust angles etc.. low speed is a chore for you simply because wing loading is way higher than foamies of the same size
lots of expo and practice in holding in proper power will get you going .