Why can't the restoration process do the defragmentation itself? the software is basically creating a new partition layout, new MFT and new Filesystems...
Doing the defragmentation on the original server is not possible when it's a recovery case and when resources are limited it can become life saving for this functionality to be working properly.

Anyhow, one can extend the question to : if there can be a problem with the minimum size requirement, why is not displayed properly in the creation of the plan instead of just the used space?

Cheers !