Photo iCloud optimisation not working.

Hi, here's the scenario. I had 270 ish photos viewable on my ipad while using the optimise with iCloud storage feature and the storage on my iPad was being optimised. I had roughly about 9GB spare . A few days ago I deleted all my iCloud photos and videos and reuploaded them again (wanted to manually remove duplicate photos). Now when I view my iPad on iTunes the spare storage space is about 3GB. In the settings I had optimised between iCloud and iPad checked and I've disabled and enabled this feature a few times incase that was the problem, unfortunately though the storage no longer seems to be optimised and now there's much less space on my iPad. If anyone has any ideas to fix the optimisation that would be great as it's always nice to have space to stockpile movies for a long journey, thanks.