Upgraded boot drive - which heatsink goes on which SSD?

Upgraded my boot drive from a Silicon Power UD90 to a 2TB WD SN850X and cloned everything over. Planning to move the old UD90 down to a secondary slot for extra game storage.

Board is an ASUS TUF Gaming B650E-WiFi. I also have a be quiet! MC1 cooler sitting around, but not sure which heatsink should go where.

Would the MC1 be better on the boot drive or should I go with the motherboard heatsink?