I'll be darned. I'm using the same object at Cascade Creek Hydro ... and it sits right on top of the platform. We'll have to think about this one.
Update: If you go to slew mode, and go "up" then set it back down does it stop on the surface? This may be related to another problem I'm seeing with ADE. I'm trying to make a starting point on top of a dam, but I cannot get ADE to recognize the elevation, so it starts at the base of the dam. This could be similar, something to do with the starting altitude (which I've ben unable to manipulate so far in ADE). Let us know on the slew, that would be a clue.
Doug