I may have found the issue here.
I was curious as to why FOG was refusing to resize the disk, so I thought I’d try a manual resize in linux/gparted. Booting in to the gparted live cd, gparted could see the drive and all of the partitions but it was failing to read the contents of partition 4.
I Googled this and it looks like it may have been caused by bad sectors and running chkdsk /f had fixed it for others so I tried that, went back in to gparted and now everything looked fine. So I’ve run a new capture and it appears to have shrunk the 4th partition as expected. I’m currently deploying it to one of the drives that was failing and all is looking good so far.
I’m not sure what caused the issue in the first place, I hadn’t modified the partition table at all, I had just installed an admittedly fairly large number of programs to an existing image and tried to recapture it.
@Quazz @Sebastian-Roth @EduardoTSeoane Thanks for your help on this folks!