I've been looking at the helmet I have and the photos of the ear pieces. This is the central piece of the helmet to be sure, with the most detail work, inset pieces and the part that need the best fit on the helmet.

I'm figuring out how they were made originally, retracing in my mind how the designer thought. The trick is how to plan the CAD design work to get the most out of the 3D-print and still look like the original.

What I figured out is that I don't need a perfect fit to the helmet after all, meaning I don't need to scan my base helmet for geometry.
Because the helmet is flexible plastic I can approximate a simple angle and let the inside of the ear piece following the helmet edge be straight and flat. This simplifies the work a great deal!

When I have the pieces I can show how this works.