Is your 90degrees at the surface of the substrate or the glass below it? If its of the glass below it maybe you might want to consider that your substrate layer is pretty thick (since it is, after all, thick enough for it to hide in). If this is the case, what is the substrate surface temp as well? I only use half inch of substrate at most. They push it aside yes, but its never enough to hide under. If the 90F is the substrate surface, start measuring the glass surface that he's sitting on when he gets under the substrate. It might be hot.