We probably don't need another thread on this title. See:
https://forum.blu-ray.com/showthread.php?t=10957
There are no BD or HD titles that are CBR - they are all VBR. CBR isn't a smart thing to use for modern video. This title is total overkill on bitrate already, so you are basically judging the original source material. It may not be to your liking.
Anyway, you may want to stop looking at the inaccurate bitrate meter to weigh quality. Even if it was "live" accurate (which it isn't), it's pretty much meaningless; easily compressed sequences will always have lower bitrates when the codec is doing it's job.