Runway float above ground....!

Can anyone help me? I want to make my own fictive airport, in an area, which not have any airport in the real world.I use FSSC, there I have flattern and excluded an area, there I want my airport. I have flattern the ground to 0 feet above sea level. And thats work fine. The ground level is then 0 feet in FS2004. I then place the runway at the flattern area (also with FSSC), set the runway preference to 0 feet,but the runway is floating in 16 feet, which is the standard height in FS2004 in that area.I have also tried to use AFCAD, to place the runway in the area (still with the flattern used in FSSC), but it's the same. The runway is floating 16 feet above the ground.Can anyone help me?Best regardsHenrik