I’m learning how to bake ambient occlusion… In this model no matter what I do the shadows are no larger than than the ambient geometry… (rails). How can I increase the size ? This is for export into SL…

To me it looks like it’s too large with the default attenuation of 10 (blender units) so the occlusion gets spread out on the top part quite evenly. Perhaps try with lower value.

Bottom left: original, bottom right: bake with lower attenuation. Object scales have been applied with ctrl+A -> scale, too.