Stop downloading RAW to iPhone

I have set up iCloud photos on my main iMac and it is slowly uploading my images to the iCloud library. I have set my 64gb iPhone 6 to use iCloud photo sharing, expecting it to download 'Optimised' images but as well as smallish JPEGs of some images, its downloading un-optimised, full size RAW files to the phone. I know this because widgets like Dropbox or Image capture can show me the size/format of the new photos in my iPhones photo library.

Subsequently I've plugged the phone into iTunes and it will no longer sync and has forced me to do a clean install and recovery.

My main question is "How do I prevent the RAW files downloading and basically killing my iPhone whilst still using the 'correct' iCloud workflow?"