I ride a 2014 Ultra FLHTK that has since turned into a trike. I would like to take my dog with me and have tried two carriers that I returned each so far as I didnt use them.
The first one I bought was the Kuryackan Grand Pet Palace. When it sat on the seat it overhung the drop down to the riders seat by 3 inches. This wasnt even an option to try to mount it.
The second one one I tried was the Saddelman PC3200C pet voyager. Although it was a little smaller it didnt quite fit on as nicely as I would have liked. If you put it on one way the corners would hit the speakers and you cant get it to sit all the way back. If you turn it around it does sit better but it will still dig into your speaker grills and I am not into ruining one thing to do another.
Lastly neither case sets evenly on the luggage carrier and I would prefer him to sit on the seat.
The dog is 16 pounds.

Has anybody used a different carrier other then the two I listed on their touring seat. If so please let me know what worked for you.

 

I'm on my second Pet Palace. They last about five years- mainly the zippers crap out. My dog weighs 21 pounds. The carrier is cross ways on the passenger seat up against the sissy bar. You are correct about the overlap. I took a piece of thin plywood- luan, covered it with that thin blue insulation and attached it to the bottom of the carrier with construction adhesive.Works very well.

 

Not mine, but seen at a Sunday cars & coffee sorta deal...