Images keep getting blown up way larger than I think they should be

I’m new to this SuperNews theme, and WP in general, and have been working to get it up and running to my “satisfaction”. One issue that is really bothering me is that when I click into post entries, the featured image gets blown up way larger than I feel it should be, and it consumes so much of the page that someone cannot even read the content without scrolling. I don’t like that.

I have gone into Settings -> Media and changed the image sizes to the following:

thumbnail – 240×240 cropped
medium – 400×400 cropped
medium_large (listed in Acme Fix Images but I cannot find a place to change it) – 768×0
large – 500×500 cropped
post-thumbnail – 240×172 cropped

I have followed that up by having Acme Fix Images go out and fix everything that exists. I have not, however, noticed any difference in the final size before the parameters were changed and after.

As an example, please reference https://www.godwin.org/wp/2017/02/13/tweaking/. The image on that page is 300×275 native but it is being rendered on the page at 623×571. Similarly, the featured image on the page https://www.godwin.org/wp/2017/02/10/what-does-ha-mean/ is 400×384 native but is being rendered at 623×598. The x value of 623 seems to be the common denominator here but not sure why or how to change it.

Please forgive the “simplicity” of my posts on those pages; they are mainly practice in attempts to get everything to my liking. Thanks in advance for the input.

Mike

p.s. I’m running current versions of WP as well as the theme.