It pretty much matches right up with the back of the top of the solo seat back. Don't know where the "standard" passenger seat would sit, height wise. I don't feel any new lower back support.
Strangely enough, this is the first bike I've never had the desire to buy an aftermarket seat. I can go 300 miles with no discomfort on the Vic solo seat.
'09 Kingpin 8Ball
'06 HD Road King
'06 Vulcan 900 Classic