We like to place the disc just below center. As you described, about 1/3 up from the decal.
I don't think that Goldwing cams "walk out" under acceleration but many cams or distributors do. By positioning the encoder a bit low, the disc will never contact the reader under throttle. I do this a bit by habit.
Also, if the customer did not install a base gasket on the housing, or a cam was slightly "tall" compared to most, you can always use a shim washer to raise the encoder. If it was too tall, you'd need to mill or sand it shorter. Not every customer has the tools to modify a spacer.
Good eye Joe! Thanks for posting this so others know what to expect.