That’s because -cq is not recognized by MCEBuddy. It’s a deprecated option in ffmpeg and it doesn’t mean constant quality as most folks think. It means constant quantizer, very different from constant quality.
You should either use the -b for bitrate or -crf for quality. MCEBuddy recognizes both and will adjust the values when you move the slider.
If you don’t want MCEBuddy to change any of your video profile parameters (including ignoring the quality slider) add the necessary VideoOptimized directive to your profile. See this link for more details: MCEBuddy - Advanced Settings, Commands and Tweaking
When creating custom profiles refer to the above link and also feel free to check out existing profiles for examples.