You might trying playing with the parking center and radius, the Stop position, the deicing area radius and, most importantly, the "Distance Threshold" parameter of that particular gate.
Your goal is to set the radius of the Parking and the Deice area in a way they won't overlap, and adjust the Distance Threshold ( which is what makes GSX decides if you a "in" a parking ) if required, so GSX will recognize the parking and the deice areas as different non-overlapping zones.