Featured image weirdness

I am seeing very erratic behavior in the featured loop images in my MiddleEarth theme.

When I upload 240x240 pixel images for the loop images, in some posts the image will be displayed as a square like the original image, and occasionally it will appear as a 210x126 pixel image, being cropped at the top and bottom.

Changing the values in the MiddleEarth control panel inside WP doesn't seem to have any effect on these strangely cropped images either, while the ones displaying in their original aspect ratio are affected.

Can someone please explain to me what the approach is to these loop images, and what I am overlooking or doing wrong? What are the best dimensions or aspect ratios to upload these images?

Hi, the following link should help you:

http://www.studiograsshopper.ch/web-development/wordpress-featured-images-add_image_size-resizing-and-cropping-demo/

I have slightly different question: the proportion of the featured image is OK, but it is displayed too small. Is there a way to change the size to be displayed? Check what I mean by looking at this page of my site:

http://theologos.net/b5/en/end-time-books/midnight-cry-waking-up/

Well, got it. The featured image is called loop image and I set the width and height allowance in reversed order. That was why. Now everything is good.