Why is my iCloud Photos library smaller than my Mac Photos library

Ok, so I just upgraded my iCloud storage to make it large enough to hold my Photos library that is on my Mac. My iCloud settings in Photos is set to "Download Originals to the Mac", which, as I understand, means I keep full resolution copies of all of my photos and videos on my Mac as well as on iCloud. When I started the setup, by going to my System Settings I could see that my iCloud "Photo's" storage was growing as my Mac was uploading my photo library to iCloud. Now, since last night, the size of my Photo's section on iCloud has not changed but the size that is showing is significantly smaller than the size of my Photo's Library on my Mac.

Here is my iCloud account

Here is my Mac

As you can see it is 23.12Gb on iCloud vs 32.89Gb on my Mac. My question/concern is that either my Mac has quit uploading my data (no, I've not pushed the button "Pause for one day" on my Photo's preferences) and/or there are files missing online that I have on my Mac. Unless Apple is using some other super compression that they have for their online storage that you as a user do not have on your Mac I would expect the size of these to files to be approximately equal with the size of my Mac storage to be smaller if I enable the local optimize feature.