As explained many times already on the forum, related to any scenery (because it's an FSX rules) AI park first depending on the parking radius, they will go in smallest parking which is large enough to fit their radius. If multiple parkings are suitable, they will be assigned following the atc_airline_codes in the AFCAD IF they AI have their own atc_parking_code in their aircraft.cfg.
If you are seeing a plane too large to fit in a parking, it's possible the radius in that AI .MDL file has been set too low, some developers (especially in FS9, and WoAI IS made with FS9 models, which is a reasons why it would be best not using it, for fps/memory reasons) set non realistic radius ranges on purpose, to make up for the lack of usable multiple atc_parking_codes in FS9, but this is not needed in FSX.
And, as explained many times on the forum, the parking radius we set in the AFCAD, has an effect on jetways too so, it's *possible* that we might have set it higher in some places, because otherwise the jetway wouldn't work, of course it's best having all jetways working and accept some unrealistic AI positioning, rather than have a malfunctioning jetway.
But as usual, whenever you report what you think is a problem, please be very precise about it: please indicate exactly which gates you saw AI that shouldn't be there, so we can check the gate, the size, the atc_airline_codes and the jetway, and explain or (if needed) fix.