I found 3 relevant effects but I'm not sure what I'm doing wrong because it's not making any difference.
There's also 3k_dlc05_effect_dummy_reveal_adjacent_regions for the assignment which is not quite what I want but I couldn't get that to work regardless.
I am trying to add line of sight buffs to certain buildings, such as Ma Teng's military building. I tried exhaustively using one of the above effects, and combining it with different scopes but none of them had any effect after I loaded into a save. Same fog of war.
I tried all the variants to region_to_region, region_to_province, province_to_province, building_to_building, etc, but no combination made an impact to how far I could see, despite it showing up on the building card, that I am supposed to have +XX% county or commandery line of sight.