When you select to "Grouping By Program Name" but do not select "Open groups in popups" then the tile is somehow shorter even when there is a lof of space empty.
Created attachment 103919 [details] Bad width (to short)
Created attachment 103920 [details] Good width
It's intentional as inline grouping will generally more task buttons, to avoid the layout changing very often.
Created attachment 103924 [details] width fix. Somehow it is exactly oposite, for me if i have one chrome open first, terminal second, and then i will open second chrome, i want chrome to get after the first chrome so in between chrome and terminal. You probably will say than you can order Alphabetically, then no, because if I open NEW window, it often gets before the previous one. (example, i have "Terminal <9>" and i will open next one then "Terminal <10>" gets before 9... I don't like (even hate) this popup groups, but i ... LOVE the grouping, so whenever i open new X it will be placed behind X on the task list. And if I do it like on "bad width" screenshot, i get the ability to REORDER the gorups, still having them to group togheter, Yes, i know, it's like f... W10. The problem is i HATE W10 but i like their grouping behavior. And i love Linux & Plasma it's f... awesome! So for anyone else that want to have the same size here is the patch. Simple comment-out line "return preferredMinWidth();" in function preferredMaxWidth() in file /usr/share/plasma/plasmoids/org.kde.plasma.taskmanager/contents/code/layout.js