The blog posts use a “wide” version of the Post featured images (1200×600).
The resized ones that go into the (3/4 content + 1/4 sidebar) default blog layout get to be around 891×446 so it’s not much of a size difference, having them in the full layout size gives flexibility in the future though, provided you want to change that layout etc.
Feel free to change the default blog size though if you really must, it’s in your functions.php:

add_image_size('boc_thin', 1200, 600, true);

Don’t forget to Regenerate Thumbnails if you do so… There are plugins that do that for you.

I would concentrate on optimizing my images instead though, also make sure you use CACHING & Minification plugins to optimize page load times and overall resource sizes.
Good luck!

That definitely should not be the case… There’s a designated size specifically for this custom widget, it’s 150×150 and it’s defined in your functions.php:

add_image_size('boc_thumb', 150, 150, true);

That’s what the size of the images that come out there should be, you can check the Demo for reference. Was this an installation that previously used a different theme? Maybe the new Fortuna thumbnails have not yet been generated? If that’s the case make sure you run this:

https://wordpress.org/plugins/regenerate-thumbnails/

Check here at the bottom for more:

http://blueowlcreative.com/docs/fortuna/#installation1