@bhajyna
I prefer the horizontal bar, so I didn't notice this until your post prompted me to check. I also didn't notice the blog post on how vertical tabs work, which says that the "Tab tooltip" isn't available in vertical tabs, so features which depend on it, such as the volume booster, can't be used in the vertical layout.
ETA: However, volume booster levels set in the horizontal bar appear to "stick" after switching to the vertical bar. So, while you can't use the volume booster control with vertical tabs, you may be able to use the feature if you set a tab's level in the horizontal bar.