Sorry, reading the posts I thought this was a commonly acknowledged issue. When using either the AVIA builder or the shortcode, when you select BLOG POSTS and then select the option to “Preview Image Size – Set the image size of the preview images,”

regardless of what size image you choose, it still displays a huge (usually unfocused) version of the Featured Image.

http://sweetlizzydesign.com/blog-post-image-test/