Theater movies vs storage

Hello,

I am having difficulty to understand how iMovie handles movies. I have created movies, exported to external HDD and iCloud Theater. When I looked at my storage on MacBook Air I realized that iMovie keeps movies in iMovie Theater folder and blabla /Library/MobileDocuments/iMovie/Theater/Media.

Now the confusion.

I exported movie in high quality, 15min movie 2,3GB 1920x1080

the same movie in /Users/me/Movies/Theater is 1,12GB 1920x1080

and the very same movie in /Library/MobileDocuments/iMovie/Theater/Media is just 570MB and 720p

Why is that? I understand that 1,12GB file is enough for playing (I think Theater plays this file)

Why is there 720p was it uploaded to Theater for playing on iOS when I choose no HD version?

If yes why iMovie did not clean this file?

How can I clean the storage?

I know I can try Optimize storage but everything from Theater will be unreachable unless I untick Optimaze storage again and it will download every single movie.

How you handle this?

Cheers