FCP optimising media (Canon Raw Lite) to ProRes 4444

Hey folks,

I have a project I'm trying to archive, and would like to cut down on the library size.
It was shot with the Canon C200 and the R5C in its S35 5.9K crop mode.
When I choose to make optimised media in FCP, it transcodes it to ProRes 4444, which is slightly larger than the source raw files. My only other options are the H.264 or ProRes Proxy files.
Is this just a raw thing? I know that I usually get a 422 file when transcoding from other codecs.

What are my options for reducing my library size? FCP seems pretty finicky sometimes when it comes to replacing Original Media with transcoded, High-Quality Media. I used to (and still do) transcode Canon 1DC footage from MJPEG to ProRes 422 within FCP and then just replace the original files with the transcoded files with no issues, but FCP doesn't seem to want to do that with the raw files. 
I've tried transcoding to ProRes 422 in Resolve and then relinking those files, but FCP won't bite. It's the same thing with optimised files created within FCP itself - if I try to stick those files in the Original Media folder it won't recognise them. (And then I'd be left having to re-transcode them from ProRes 4444 to 422 anyway...)

Ideally I'd like everything in 4K ProRes 422 - even the R5C 5.9K footage. 

What are my options? Or am I hooped?

Thanks~