Then there is the Tector-class which is visible for a second in the Endor battle scene, it has a reinforced reactor and no hangar bay.
The FFG model is that of the ISD-II
I think they didn't actually make a separate model for the Tector - but took the big Avenger model, and did some custom work on the underside - removing the reactor dome, covering over the hole, and covering over the hangar bay.
Same thing they did with the MC80 by adding wings .... I think? But, anyway, Lord Tareq is right, it is a seperate ship shown on screen. So, FFG totally needs to make one for our blasting pleasure.