multibody Sheetmetal wont flatten - any ideas why?

Hi

Have a look at this part and see if you can tell my why it wont flatten.

Its a mould for a special brick so has an inbuilt taper.

I got all this way and got it approved, only to find that I cant make it work

There are 3 parts in here. A body, a back and a ring.

The ring is simple enough.

The back flattens but at the wrong size and the body only partly flattens

Cheers

Darren

SolidworksSheet Metal