FSX Floating Apron

I am modelling my first Float Plane base. Every thing looks fine except for a floating Apron which I use for parking. See attached. Obviously I've done something wrong. Any help would be appreciated.

Thanks, Peter Hall, Vancouver Island, BC


The elevation of the Flatten and the ARP agree but I still have a floating Apron, however, I deleted the apron and put in a custom ground line with an asphalt texture and it looks OK. That still does not exolain why I had a floating apron. Would it help to see my ade4 file??