The 100mb system reserved partition contains the efi bootloader for booting windows. The windows installer will always put the bootloader onto the first disk it finds, no matter what disk you selected when installing windows. This is why you should only have your preferred drive connected during install.
You can try to move it using EasyBCD
However if you get an error then I would just create a new efi partition on your preferred drive
2 hours ago, Skipple said:
Responding so I remember to come back to this later. I'm curious to the answer. I don't even have a System Reserved partition. ¯\_(ツ)_/¯
You only get a system reserved partition if your mobo has EUFI bios and your disk is gpt formatted. See this guide for converting