Incremental Backup of Parallels 10 Windows7.vpm- is it incremental?

When ATI for Mac does an incremental backup of an entire mac drive on which there is a Parallels 10 Windows7.vpm, does each incremental back up equal the file size of the vpm file? In other words, if the windows7.vpm file size of the first back-up was 308 gb and the next day some changes ocured to the vpm file and it became 310 gb, will ATI for mac copy 308 gb on the first day then the extra 2 gb on the 2nd day. Or, will ATI copy 310 on the first day, 308 on the second day, etc.

My 4 tb drive that I am backing up to is almost full and I suspect it is because the latter method is used rather than the former.

What I want is an automated way to back up the Windows7.vpm file vs. having to do it manually. I would be willing to change to a max of 5 vs. 10 backups to keep from filling up the destination disk.

I may have bought the wrong product. Was the windows version of ATI installed in the windows7.vpm was the way to go?

I tried to buy ATI2015 from within Parallels 10 like you had to with Parallels 9 but could not figure out how to do so. I think that version 10 of Parallels was changed so that you need to buy ATI direct from Acronis. Long post- sorry, but I think there may be other users out there with the same problem.