How can I force all photos to be stored only in low-res on my MacBook

From reading the description on the Preferences in photos it says

"Optimize Mac Storage - Store full resolution photos and videos in iCloud. Originals will also be stored on this Mac if you have enough storage space"

The last sentence here is a big issue for me. I don't know how my Mac tried to determine what 'enough' is but basically I need free space desperately and I need ALL photos to be stored in iCloud, and low-res versions only on my Mac. No ifs ... no buts. This works fine it seems on iOS devices but the amount of space saved on my Mac has been really poor.

Is there any way to do this?