Ok, anyway, no problem, really - I try to explain my needs, maybe someone can help (see my example capx):
1. My player must have a clear LOS to every object he is actually spotting (i.e. to any vehicle of the first row), as happens in the real world. To achieve this, no object can be Solid or defined as “Obstacle” by events. Strange, but... ok.
2. Objects hiding behind the “big cats” in the first row must be out of player’s LOS, as they are covered (think of infantry hiding behind tanks). Again, nothing strange here, this happens in real world too. But if the green tanks are neither Solid nor defined as Obstacles they are (correctly) “transparent” to player’s LOS.
It's perfectly possible there is a simple workaround, but at the moment I’m not able to see it….