Equinox rear tub on a std Haynes rear frame?

[Nickp]

I'm trial fitting my bodywork to try and get it right before painting my chassis. I've started with the rear tub which is a bit of a PITA TBH!!
I've got it fitted nicely around the roll bar and it sits snugly on the top rail of the frame but is a good 1.5" off the bottom rail, leaving a big gap. Are there revised frame dimensions for the Equinox tub? It meets the front of the bottom frame OK so I can secure it there and I can fasten a couple of tabs on to secure it at the rear.

So should I be worried about this or just crack on and work around it?