Hey Gunter,
“””””” I'm just not
sure if it should be the outer or inner? I feel if I use the inner unwarp, it might to too small?””””””

Taking the thickness into account is a bending thing as metal doesnt bend with exact dims. But for your cone unwrap, it will only affect the “seam” and it will have an “angle” instead of original flat ends.

When you coil your cone, the first part to touch will be the inner edge and you will be welding the seam shut on the outside.

For most accurate results, use the inner surface as your unwrap, then bead and fill the gap on the outside.

In theory, if you did both unwraps, you can determine the angle of the ends and the roll your cone to have no gap when it meets. Or determine your dims at centerline or something other than….