In the attached map, I have a number of Cores directly under energy mines (for a specific reason). For gameplay reasons, the mines needed to be easily selected. However, clicking there would select either the Core or the source, doubleclick dependent. Setting the Core to be unselectable is worse (I can no longer select/move it in the editor).
In the editor, I haven't found a good reason to select the mine, and in-game, I haven't found a good reason to select the source.
I know what I expect to happen: click on a mine (highest-layered image) and it is selected. I expect either that doubleclick would select all units, or that further clicks select the next unit. Also, that the editor allow Cores to be selected.
Anyway, this map is impossible without that ability.
Postscript: Changing the Core size lets the mine be selected when clicked, but not on the central cell. This version, (with Core selectability enabled by the script(s) :awake function(s) for editing convenience), is finishable, but I'm raising this for the future.
Added to my list. I should have a work window coming up soon so I can take a look.