Hi,
I doubt that the Storage issue you mention is related to your Acronis issue.. Acronis basically digitally photographs the partition structure on your HDD.. Any setting that might be running within Windows would have no effect on Acronis when using bootable media... It would simply image the error along with everything else..
It is not necessary to image the entire drive for it to be bootable.. If you were to look in Disk Management at the partitioning of your Windows drive.. You would normally only need the Windows partition and any partition to the left of it.. If any.. The Partition structure can vary widely based upon whether Windows was pre-installed, clean installed, or an upgrade.. Or whether you are running Legacy or UEFI Bios..
Now that I think of it, it would be helpful if you could post a snapshot\snip of your Disk Management partitioning screen.. I could better advise what may be needed.. For instance... You could image only a small partition on your drive just to see if it will work without spending 5 hours.. It may not be of any use otherwise, but would answer questions.. You could possibly isolate which partition may be causing the problem..
The problem with Windows Defrag is that it does not show or list individual files so that something unusual can be determined.. You could have 100gb of garbage files on your HDD that you would never suspect and would not be listed in the properties of the partition.. I have encountered this personally several times..
I just created a Acronis 2016 image of my Windows 10 (2004) with all updates and everything went normally... Acronis 2011 also worked normally... My current setup is using Legacy Bios though.. It is possible that I could get different results if using UEFI Bios..
If you are using UEFI Bios, I can switch over to that and check..
I am not suggesting that Acronis is providing a inaccurate file size.. at least not at the moment..
I am suggesting that Windows may be providing a inaccurate file size, making your estimates of the space needed for the image incorrect..
Post that picture of your Disk Management.. It would be quite helpful..