Photos taking up 8GB of storage w/ iCloud Photos enabled

Hi all,

I recently purchased 2TB of iCloud storage, uploaded my entire photo library to iCloud (40k images), and enabled iCloud Photos on my iPad w/ "Optimize iPad Storage" enabled. Still, Photos is taking 8GB+ of storage on my iPad. I also can't enable iCloud Photos on my iPhone since it only has 3GB of space available. When I enabled iCloud Photos on my iPhone, my phone ran out of storage after about 30- minutes - I had to shut off iCloud Photos.

I was assuming that when iCloud Photos is enabled, the local disk cache would be a Google Photos like ~500MB, keeping a light footprint on each local device.

Other than optimize storage, is there any way to reduce the storage footprint? Having photos sync to devices is great, but if it takes up ~8GB of storage on each device, it's unfortunately not going to work for me.

Any suggestions / tips would be greatly appreciated. Thank you!

Damon