iOS Sprites in PVRTC?

I’m trying to reduce the file size of my iOS build (>100 MB) whereas my Android build is 49MB.

The app is a 2D game consisting of all sprites. They are non-power of two sprites, and are imported as single sprites (not in a sprite atlas or anything). Source images are PNG or PSD of course. I believe the difference in size is due to iOS not having DXT file size. Is that right?

My confusion is how to compress the iOS sprites. Are they automatically scaled up to a larger size then compressed with PVRTC? Or is this something I have to do (by going through all my images and making them square?)

I tried changing the Texture Type to Advanced and setting PVRTC compression on, but that appears to not work with sprites.

PVRTC can only compress power of two textures.