it's currently set in https://github.com/nicklan/pnmixer/blob/master/src/ui-tray-icon.c#L250 to

    vol_meter_width = icon_width / 8;

I can barely see the volume meter bar in my tray icon. I see two solutions here:

1. change it to icon_width / 6 or icon_width / 4
2. make it configurable

Making it configurable seems a bit like overkill to me and increases maintenance burden for a really small corner case.