Sorry to bump an old thread but I think its better than starting a new one, I'm getting the smae problem at the default Lisbon (LPPT) airport, after installing FTX global mesh and running the hight correction option.
I've tried moving them down in the parking editor with the Q&Z keys but the Marshals and parking system still appear in the air, I've tried deleting the confic file for the airport and starting from scratch but it still persists, all the other vehicles snap to the ground just fine, I've noticed in parking system editor that the blue markers for the objects are not on the ground but also higher up than normal, also have the latest version installed.
Here is a pic of the parking systems too high up.