after some more or less random investigation, I found out that the targeting was implemented via an "ammo-turret", so an invisible building is placed. that explains why it can not be placed in fog of war. in the meantime, however, the normal placement seems to have been changed as well in last versions. so you get an "cannot reach" message and now you have to press the shift-key.
As result of this investigation comes up, that I ave to rework the whole targeting system. So no fast fix is possible.
"Auto Targeting" in fog of war will not be implemented. you will always need an radar for scanning a sector.
" Manuell Targeting" could be possible with the new system, I think.