airport_visibility_panc = 4
When a small airport is interfering with a larger one, because it's too close, you don't increase the visibility of the large airport, like you did with this line but, instead, you decrease or set to 0, the visibility for the smaller one, this way:
airport_visibility_Z41 = 0
Note that, in order to work you MUST have a recent GSX update (from at least January 2018), because there was a bug in the original version which didn't recognize numbers in the icao code for the excluded airport but, it has been fixed in the January 2018 update.