Then, after that you can just clone your C: drive partition to the remaining space. The efficient way to do it is to have the target drive with the 16 MB Microsoft System Reserved (MSR) partition, followed by a 100 MB FAT32 EFI System Partition (ESP). However, there is a more efficient way, but to set it up nicely you will either need to repartition your target drive or use a tool like MiniTool Partition Wizard Free to create empty space on the target drive in front of (to the left of) the existing clone of C: drive on there.

Then you may need to boot into a Macrium Reflect Rescue Drive and under the restore menu run the utility to Fix Windows boot problems to update the EFI system partition with the partition information for the cloned Windows C: drive partition. How do I fix that?Since you asked previously how to do it with Macrium Reflect, you also have to clone the 100 MB FAT32 partition along with the C: drive partition. with the same product key, available in the same computer at the same time. I think the problem you're having is that you are trying to have TWO Win 10 installations. IF something happens to your Win 10 installation, then just put a spare drive in, and restore from the backup. Leave the newly created standby drive, out of the computer, until you need it again. If it works, then take THAT drive out of the computer, and put the original Windows drive back in.

THEN check that you can boot to the standby drive, you just reastored Windows, to. Take the drive with Windows on it, out of the computer, boot from the macrium USB stick, and 'restore' the backup you just made to whichever drive you want. Make a full OS image backup of your Windows install (letting Macrium choose what partitions to include), and save it somewhere. If you want a standby SSD or HDD with Win 10 clone on it, then do it this way.

How can I do that (with Macrium Reflect)?Here's the way you SHOULD do things.

Macrium reflect clone windows 10