Lighbox to original image does not show full resolution

Hi

I struggling with picture popup size on my page.
My setting for media to resize the originial picture is 1600*960 px. This is working

Now I would like to have the popup (lightbox?) on my site with the original picture size:

https://new.michael-joos.ch/index.php/links/blog/test

But no matter what I set, it opens the lighbox with a smaller resolution (but the link to the original picture seems to be ok)

Please see my settings in the uploaded screenshots.

Thanks & BR
Michael