Ctrl + SHIFT + click does this, for: mirages, prism tanks, flak traks, apocalypse... and any other unit (including infantry) that does not fire while on the move.
Ctrl + alt + click makes a unit guard/follow another unit.
Thanks mate.
But still puzzling to understand how ctrl+shift+click differs from just click. I just tested and as far as I know both ways the attacker kept the same distance from what it attacked. I tested with prisms and mirages.