The square thumbnails in the list of results has always the same size in pixel. Why they don't have CSS fixed to this fixed size?
The layout of the page is changing as the thumbnails are loaded, it is disturbing.
Also - in the recent version of IIIFServer - we have added /square/ size request. So in case we upgrade you could use better request to retrieve the square thumbnails which preserves the aspect ratio without deforming the image inside.