I'm not sure this has anything to do with GPs. I can't be sure because you have used custom textures which I don't have, so it won't compile.
However, I did notice that you have changed the ARP elevation from the stock value of 81.31m to 81.97m. Did you put the elevation stub generated by ADE into your Scenery/World/scenery folder what you are seeing is expected.
Orbx "stuff" installed as directed tends to override everything else - ORBX's intent but not good if you have other scenery packages - and may be overriding your elevation stub. Try disabling the ORBX stuff and see if the problem persists. Also, before doing that, check the ground elevation where you are having the difficulty. If it's not exactly the same as your ARP, that's a clue.. Should that be the case, then try changing your airport elevation to agree.