Same file sizes while using different quality settings

I've exported five versions of an about eight minutes long movie that I've made with the only difference being which alternative I've used in the quality drop-down menu in the export settings (Least, Low, Medium, High, and Best). I'm exporting MP4 files using the H.265 compression. The resulting file sizes are as follows:

- Least: 67 MB
- Low: 1093 MB
- Medium: 1125.803 MB
- High: 1125.803 MB
- Best: 1125.804 MB

Is this to be expected? Is it likely that I'm doing something wrong?

I haven't seen documentation of what the difference between medium and best are. But even 'Best' Quality is pretty bad.

The Documentation of the encoder settings is completely non-existent in the 3000 page manual. I would be interested to use the variable bitrate h.265 option resolve has. But with zero explanation of what the various options are, I just use handbrake with DNxHR exports out of Resolve.