Yes, Copy-NaHostFile leverages flexclone for files, aka sub-lun cloning. If the source VHD is properly aligned, and the reference limit for a block hasn't been exceeded the clone will exactly match the source. If the source VHD is not properly aligned the entier VHD will be copied. Any block that has reached it's max ref count will be copied. With those two exceptions no new blocks are written the cloning operation is just a bunch of pointer manipulation.