The Activity Manager applet always pops-up from the bottom. However if you have a side or top panel, that location is quite far from your actual mouse position, i.e. you have to move your mouse quit a bit.
So it would be nice if the Activity Manager would adapt to the location and pop from the left/right side or top.
I can attach a screenshot if necessary.
This feature request was filed for KDE Plasma 4, which reached end-of-support status in August 2015. KDE Plasma 5's desktop shell has been almost completely rewritten for better performance and usability, so it is likely that this feature request is already implemented in Plasma 5, or is no longer applicable.
Accordingly, we hope you understand why we must close this feature request. If the requested feature is still desired but not implemented in KDE Plasma 5.12 or later, please feel free to open a new ticket in the "plasmashell" product after reading https://community.kde.org/Get_Involved/Bug_Reporting
If you would like to get involved in KDE's bug triaging effort so that future mass bug closes like this are less likely, please read https://community.kde.org/Get_Involved#Bug_Triaging
Thanks for your understanding!