I don't know what that is with the weird "default" values either, or if there's any logic to it, but it did call enough attention to itself for me to realize that I could change the value.
Instead of using the slider, just input the value that works best for your player. (The same goes for the audio level. I like round numbers so I just input "150" % to boost the volume on the audio track.)
NOTE: Be carefull about going too high in the bit rate, you need to stay within the playback specs of your device. Otherwise you'll end up producing a really high quaility rip that can't be played on your portable.