What's going on here:
I have 3 second HD prores 4444 clip in my timeline. I export it and it's 106 MB (data rate 264 mb/s).
I have the exact same shot, same sequence, same settings, only in this case it's been brought into the timeline via a multiclip. When I export that one, it's 100 MB (278 mb/s).
I examine them both in Inspector. Identical information (except as above: size, data rate, and file name).
Why the different data rates / sizes?