If you want constant quality, it's better to also encode using quality-based encoding instead of bitrate-based encoding. It allows rh encoder to save space where there's a non-complex scene and use more in more complex ones. It might, for example, be able to encode the few seconds of back screen at the begging of some movies in 50KB or something similarly small where bitrate-based encoding uses the full bitrate generating multiple MB.

This way you can easily get a 4K encode down to 4-8GB. Animation compresses incredibly well without percievable quality loss. Anything with grain will quickly balloon in size. Something like Star Trek (2009) with its insane amount of noise is more than twice that size if aiming for VMAF >95.