That’s always going to happen, any surfaces that are downward facing will have some extra resin cured on them, this is due to the inability to prevent the light source from curing beyond the current layer. Since the light is going through the layer it can cure extra material on the underside. The effect is more pronounced on areas where the resin gets into corners since the resin isn’t able to flow as easily. For gaps, if the surfaces are close enough then they can get filled in for the same reasons.