I agree with the original poster and the issue is not completely due to number of solid layers.
I have found that when transitioning from a solid layer to an infill layer OR vice versa, that the orientation of the infill does not change. This does not cause too much of a problem when infill goes on top of solid, but when a solid layer is built upon an infill layer, then this is a big problem. It means that only the lines above the infill are at the true layer height as other lines drop into the gap. This gap propagates throughout the solid layers somewhat - although subsequent orientation changes mitigate the effect. So increasing solid layers helps. But essentially there is a 'lost' or 'useless' solid layer in there.
I believe that S3D has a bug here and that the first solid layer above an infill should change orientation with respect to the previous infill layer.