Yes, nothing suits everyone, just like cameras
The size of the thumbnail display is baked in, I can't change it. CR guy had the forum Mod installed to give members flexability to post images to a common place, and I'm enabled to administer it. There is also a personal gallery which allows easy reference to larger images than the forum allows. Right now, the largest image size is 4048 X 4048, I was afraid to set it for larger until I see how much disk space is used.
It is possible to auto generate a post with a thumbnail image in it, the issue is that when I added 50 images last night, it created 50 posts, each with one thumbnail image. I spent a while removing all of those posts.
I've requested some changes to make the automated post have a larger image, but the forum does not yet have the latest version of SMF gallery.