Andersen Ultimate center of weight vs rear axle

The added distance the pin adapter adds doesn't affect the effective center of gravity for the pin weight. It's just the ball position, which with a ball mount Andersen in my Ram resulted in the weight being carried approximately 4 inches behind the axle. When I had an Andersen I can't say I noticed any handling issues at all, and the actual weight balance on your truck axles on changes a few pounds, far less than you would think.

I when I got rid of the Andersen and bought a B&W hitch I ended up adjusting it so the weight is being carried aft of the axle as well and it too handles well, wind, winding roads, icy roads, doesn't matter tracks reliably, predictably, issue free.

You won't notice any difference in handling with the pin weight zero over the trucks rear axle vs just forward.
On my short bed trucks I always set the 5th wheel pin or GN ball zero over the rear axle. No handling issues and it gets the cab the farthest away from the Goose neck or the front corner of a 5th wheel trailer while turning forward or backing.

We used the Andersen (rail mount) in a Sierra short 6.5 short bed to pull our fiver. We had the hitch with the ball in the rear-most position and the adapter turned so the socket was behind the pin. This put the weight just slightly behind the rear axle but shortened the swing radius of the pin box - which was what we needed to clear the bed rails on the sides in a tight turn. Handling wasn't an issue and we had no problems with cap-to-cab clearance on turns with our Grand Design Reflection. I'm speaking in past tense because we just traded trucks for a DRW long bed and had to get a different hitch to fit the Ford OEM puck system. I'm still a big fan of the Andersen, though.

Rob

Weight does not change, pin weight is the same regardless of pin placement. Pivot point is supposed to determine handling, but even the Sidewinder with it's much larger offset doesn't seem to have a handling issue. So 9 inches should be fine.