@Corrco Sorry this topic has been kind of lost probably when we had some issues with the forums not long ago.
The only thing I can imagine is the partition cannot be detected and captured as NTFS. In this case FOG uses RAW mode which will result in a much larger image file. This could happen if the drive is encrypted with Bitlocker or some other forms of disk encryption. Though we added a check for Bitlocker a fair while ago and it should print a message and bail out.
Please post your FOG version and let us know if you need further help.