Al, I would rate your cover at 2 cents letter rate + 10 cents registry fee, return receipt is free at this time. Thus a 1 cent overpayment. Do you have a better explanation?
More broadly, one of the challenges of a proper "solo" use of any of the 13 cent stamps from 1900 to the advent of the 3 cent letter rate in 1932 (and the brief war rate of 1917-1919), is finding an actual combination of postage/fees to come exactly to 13 cents. The registry and special delivery fees start at 10 cents.
As a tangent, Scott 308 with a registered foreign letter naturally adds to a solo use (5+8=13) prior to the increase of the registry fee from 8 to 10 cents on November 1, 1909, but it gets hard after that as 339 has only an 8 month window for a similar use.
