it look like there is a minimum height when you have an vertical icon only task manager cause the icons are small, but the distance between the icons are huge. if the vertical panel is width the icon only task manager could use two column instead of one with huge padding. Reproducible: Always
Created attachment 96564 [details] small width vertical panel with small app icons but huge padding between them
Created attachment 96565 [details] width vertical panel with large icons but horizontal padding instead of two colomn
I can confirm this on the latest release (6.4.1), but I'm not sure what should be the default behaviour.
look way better. will close this bug report