Ah ok. As it happens, I actually learned something about Reflect myself when I was tinkering with that option after reading your original post. I had assumed that using that option would work as well, but it doesn't, and after experimentation prompted by some seemingly bizarre results, I finally figured out why. "Copy selected partitions" does not
automatically copy partitions to the first available free space on the destination; it copies them to the destination maintaining the same start and end sectors as existed on the source. For typical image restore scenarios where you're restoring to the same disk from which the image was originally captured, this consistency means that any selected partitions will restore precisely on top of the current "instances" of those partitions on the destination, which is what you want. But in customized restore scenarios like yours, that may NOT be what you want. In your case, your image file contains a single partition that starts at the beginning of the disk, so selecting "Copy selected partitions" would cause Reflect to "stage" the restore such that the selected source partition would be placed at the beginning of the destination
disk -- and when any partition staged for restore overlaps with an existing partition on the destination, the existing partition gets slated for deletion. You see this when the destination disk's partition map changes, and you would also get a warning before the restore proceeded that listed the partitions that would be deleted if you chose to proceed.
But before I figured this out, I was wondering why selecting an alternate destination disk, then selecting my C partition and choosing "Copy selected partitions" caused some (but not all) existing partitions on the destination to be slated for deletion and for a small bit of space to be left unallocated
to the left
the copied partition -- answer: because some but not all partitions overlapped with where the C partition would be placed based on its original starting sector, and the unallocated gap was the distance between the end of the last non-overlapping partition and the starting sector of the C partition. I also noticed that selecting a very small partition from the end of my source disk and clicking "Copy selected partitions" triggered an error about insufficient capacity, even though the destination had plenty of unallocated space. The reason there was that the original source disk was 500GB, but my virtual disk was only 300GB, so even though the latter had plenty of free space, it didn't have a sector range high enough to place the source partition in the same location.
Anyhow, drag and drop is definitely the way to go whenever you have customized restore needs like this. Good luck!