Accessing photos in ICloud Library

I am using ICloud to backup all my photos (which I take with my IPhone6). I am trying to view them on my IPad Pro (9.2). If I choose "Optimize IPad Storage" in ICloud Photo settings and then try to view a photo, the selected photo is blurry and has a "timing clock" icon at the lower right, suggesting there is a download in progress. But the full resolution photo never appears ! Shouldn't I be able to view any photo in the ICloud Library on any device AT FULL RESOLUTION ??? If not, must I use the "Download and Keep Originals" setting ? That sort of defeats the purpose of saving space by using the Library in the first place.

Thanks for your help !

Eileen