ProRes4444 millions of colours / trillions of colours file sizes very strange

We have all-CG footage rendered to 16bit half-float and then imported into after effects as a 16bit comp. When exporting ProRes444 without alpha on the first go we accidentally left the colour depth to "millions of colours" and got a mov file of approx. 400mb file for 100 frames. When exporting ther very same clip with identical settings and only change the colour depth to "trillions of colours", the resulting file size is 50MB. Does not make any sense to me, could someone explain this? We'd like to make sure we send out the correct colour depth and the vast difference in file size has me wondering...