TIL
all plasmoids are activity specific by default (except panels which follow you to each activity) and by using desktop view you can only manually scale or place plasmoids using the edit mode.
icons/links can only be placed on the desktop in folder view, but they can be associated with a specific activity and they can be sorted and positioned using the icons tab in the configure desktop dialog.
in the configure desktop dialog, under the locations tab, you can specify to show files linked to the current activity and those files/links will appear only on those activities (sans the link icon superimposed)
only these icon/links (sans the link icon superimposed) do not seem to respond to manual sorting for some reason, but they do sort and arrange.