Cumulative impact of Photoshop opacity settings
An understanding of how the opacity setting on each layer impact results when blending multiple-exposure images in Photoshop is key to obtaining the result you desire.
If the layer opacity is too great, then those following down the stack may lose impact entirely. Conversely, an insufficient opacity setting could result in the image being overly dominated by the base/background layer.
This video provides a visual explanation of how opacity functions in a multi-layer environment, along with tips on how you can test and control opacity to ensure you achieve an optimal outcome.