About 1/2" acq...
If one fires on Inf Target Table, but not against a concealed unit, doesn't one leave a 1/2" acq counter?
When a unit marked by a 1/2" acq counter leaves LOS or acquiring firer, the counter remains in hex and can even serve to fire against another unit that comes in the hex. Thus a lone 1/2" counter can exist in a hex.
I believe that when 1/2" counter acquisition is not allowed, it is strictly against concealed targets (but a building does not enter such a category).
The difference between 1/2" and 5/8" acq counters is that the latter acquires the full hex (e.g all levels of a building) and the former only one Location.
I am not sure about my point of view, as I never try to rubble buildings (nor bridges) with ordnance - even with big guns, as they are mostly devoid of interesting ROF, I aim at units and, of course, rejoice if the whole building collapses on them [but that is as a side effect]...