f8 lite thumbnail stretching on category pages

Firstly, big thanks to the producers of the f8 theme because it’s beautiful and free and is much appreciated.

I’m working on FlipFlopsandRaincoats.com and my issue is the common one of thumbnails being stretched.

I’ve found the solution for the home page and right now, that looks lovely. But on my category pages, for example, they’re back to being stretched and weird. I can’t figure out how to apply the solution to the cat pages (or any others for that matter).

Here’s what I tried successfully:

On the 7th line you should find the following code:

<?php get_the_image( array( ‘custom_key’ => array( ‘thumbnail’ ), ‘default_size’ => ‘thumbnail’, ‘width’ => ‘310’, ‘height’ => ‘150’ ) ); ?>

Replace thumbnail with post-thumbnail, you should have something like this:

<?php get_the_image( array( ‘custom_key’ => array( ‘post-thumbnail’ ), ‘default_size’ => ‘post-thumbnail’, ‘width’ => ‘310’, ‘height’ => ‘150’ ) ); ?>

Here’s what I’ve already done/doesn’t work:

Making any edits under settings > media (i.e. uncheck box “Crop thumbnail to exact dimensions” or change width allowances).
Making sure all photos are exactly 310 x 150.

Please help as it seems by searching for the solution I’m the only one with this particular issue. Many thanks!