I have been playing with setting parking designations and have found that the Asobo aircraft have in their aircraft.cfg files a setting " atc_parking_types = "GATE,RAMP" ; "ANY" / "RAMP" / "CARGO" / "MIL_CARGO" / "MIL_COMBAT" / "GATE" / "DOCK"" so basically it can park anywhere. The same applies for add on liveries such as Aerosoft's Simple traffic. I plan to correct these.
I have redone the parking at the bespoke airport EGGP and set the airline codes (also missing in aircraft.cfg) to an approximation of those IRL and am in the process of entering these in the matching liveries.
Whether or not Asobo have implemented this is therefore to be established, although I doubt it.
UPDATE:
Aircraft.cfg files for base and livery sections amanded to "GATE,RAMP", and airline codes added.
Airline codes added to the GATES (1-8 @ EGGP).
No difference, airlines still park where they want, including a CARGO spot.
VIDEO:
http://www.g4est.me.uk/videos/parking test.mp4
UPDATE 2:
I had made an incorrect assumption that the live aircraft models selected by MSFS which were then skinned by Simple Traffic (Aerosoft) were those matched to the available flyable aircraft. This has been proved false. I have since modified the parking type on all the GENERIC models to "GATE,RAMP" and with one exception where an airliner spawned at a Cargo spot, all the others obeyed the GATE parking..
Airline codes were however ignored.