We had a 12" on the bike for the two day ride home after we bought it, and got the 18" in the mail a couple of weeks later.
The wench said the 12" pushed her further forward on the saddle than the 18", and it was not as comfy. The sissy bar has a bit of angle to it, and with the pad lower it was further forward.
We kept the 18" and sent the 12" back to the dealer.:up: