I struggled with the same problem of very poor volume control of my Beat Buddy, while playing, of course, because that is when you need volume changes the most. I tried several pedals that I already owned and always had the same results: almost all of the volume change occurred in the last 10% of pedal travel. This was untenable. My solution, while not very tech savy and sophisticated like yours, got the job done. My solution is use of a very expensive volume pedal. I’ve included the link for those interested in this approach.
https://www.sweetwater.com/store/detail/StereoVol--lehle-stereo-volume-pedal