The rule for how a layer combines with the one beneath it instead of just covering it: multiply darkens, screen lightens, overlay raises contrast.
Set the drop shadow to multiply so it deepens the photo underneath instead of laying flat gray over it.
Two blend methods earn their keep. Multiply is ink: it can only darken, so it seats shadows and lets a tint sink into the image below. Screen is the mirror image, light added to light, for glows and highlights. The rest are mostly theater. Overlay and its relatives punch up contrast by steepening the tone curve, which looks decisive in a hero shot and quietly breaks the moment real text rides on top. Reach for a blend method to make two layers share one material, not as a filter to rescue a flat one.