Dynamically update AppleScript slider widget

I've created my own implementation of a volume slider widget using the "Custom Apple Script Slider Widget". The baked-in "Volume Slider Widget" works fine, but I wanted to make it more user-friendly by limiting the maximum volume to ~70% so I can be a little less precise when sliding.

I have the slider itself set up and working perfectly fine. I then realized that the left/right icons don't invoke the script itself, so I hid those and added two touch bar buttons, set the left one to Volume Down, the right to Volume Up. Works great.

However, there's one small inconsistency that's driving me crazy: tapping the Volume Up/Down buttons doesn't change the position of the knob on the slider.

This doesn't happen with the baked-in sliders (brightness or volume), meaning if you tap one of the buttons the slider also moves.

Any advice on how to approach this?

Thanks!