It is simple.

But you do have to measure the wing:
root chord
tip chord
sweep
half span.

Then do the same measurements for the horizontal tail.

Now measure the distance from the wing LE to the tail LE.

You're done measuring. Plug in those numbers and run the app with 5% static margin, then run with 15% and you'll have the CG range for YOUR exact model.

It really does take into consideration enough of what actually matters to work out a safe starting range for your exact model's CG.