Changing Bit Rates

When rendering out footage from the delivery page, when I select Automatic>Best OR a bit rate of 10,000 or 20,000, Vimeo ALWAYS tells me my bitrate is too low and shows me very different rates clip to clip. Vimeo shows me my bitrate under the warning message and it is always different for every clip. Some are 6360 kbit/s and some are other random numbers that are a little higher or lower; but they are always between 5000 and 7000. I tried to export it through the Vimeo delivery option in Resolve instead of the Custom option and Vimeo tells me the same thing.

Why is the rate changing from clip to clip? And more importantly, why isn't Resolve obeying the bit rate that I select?