Black AO on fully occluded fragments

Hi. I’m trying to use blender to bake AO textures for use in a game. What I want to do is create a mesh for the terrain, then put other objects around the scene, and generate the AO texture for the ground. But, I’m getting pure black wherever an object sits right on top of the terrain. This results in black borders on the bake. Is the any way to tell blender to ignore these areas? Eg, make them grey, based on surrounding fragments? I’ve attached a screenshot showing the problem.

Thanks, James

Has no one else had this issue? I resorted to editing the terrain lightmap in gimp (just greyed out blacks and blurred), but I get the same problem for all models. It seems really impractical to have to manually edit all of my lightmaps.