What controls the OneDrive sync client size on disk and size?

Hi,

its controlled by "Files on Demand" It is one of the nice feature of windows 10 , when its enabled for your OneDrive it keeps the files and folders in cloud online , that means there is no disk space is required on the PC’s disk for the files.

You can learn more about this ... there are advantages and disadvantages ...
http://www.rawinfopages.com/tips/2017/09/how-to-save-disk-space-with-files-on-demand-in-windows-10/

Hope this helps!

Is this what your looking for?

 

https://support.office.com/en-us/article/invalid-file-names-and-file-types-in-onedrive-onedrive-for-business-and-sharepoint-64883a5d-228e-48f5-b3d2-eb39e07630fa 

Not quiet sure what you are referencing here. OneDrive will be smaller than the files you have in it if you have Files On-Demand turned on, which only keeps metadata about your files on your computer until you need them then it will download them.

Are you sure you have the right user profile selected where your files are? If you are copying and pasting files then it seems like you just have the wrong location that you are searching the space for. If you click the sync client and go to the folder connected to it, see what the space shows there.