Thank you for sharing this advise. Combined with the ‘auto’-Option, this is somewhat useable for the reasons you describe. Additionally, also the Navigation-Arrows do not bounce up and down.
For my application, I meanwhile use a gallery (here, the ‘fixed’ option works the way one should expect it and resizes the images to a good size. I also need to only show two images while the gallery features more images. In https://theme-fusion.com/forums/topic/lightbox-gallery-with-only-two-feature-images/ I found a solution to hide all but the first n images.