In this version of KDE (Leap 42.2 / Plasma 5.8.6), the window list (group) only fills up to half of the screen height.
If you open more windows, they are going under the taskbar.

Can I use the full screen height somehow, as it was in 13.2?

Or can I tell KDE to open a new group, once the first is "full"?

Please see the image below. Thank you.