I've never really had to mess with image services on nostr:npub12vkcxr0luzwp8e673v29eqjhrr7p9vqq8asav85swaepclllj09sylpugg...
My caching service is just the default primal one if that means anything.
I know on Amethyst, it uses nostr:npub1nxy4qpqnld6kmpphjykvx2lqwvxmuxluddwjamm4nc29ds3elyzsm5avr7, but primal seems to handle all that behind the scenes.