image sizes not displaying correctly

Greetings I have hit a wall and after many many hours have admitted defeat and hope someone has some insight

I am running Gridmarket on a multisite install and am trying to figure out how it is interacting with the plugin from MarketpressThemes Dynamic Grid (I know this isn’t your product). The issue is that I am turning this Grid into a fixed grid; it is usually a masonry grid. The problem is that the image sizes are not displaying at the same size and are cropping so the fixed grid won’t work.
I have been in contact with the plugin developer and he says that I need to upload all images in the same size and keep cropping on. This is a bit of an issue since this is a multisite, but on my test site I have created a custom image size that is the same size as what needs to be displayed and regenerated all images. My custom image size looks fine and shows the complete image.
I have then changed the function that should control the image output but still images are different sizes and are being cut off.
I am at a loss on what to do and would appreciate any insight.
If you need access to my site it is enabled.
Thank you
Meriam

Here is the code that seems to pertain.
From the plugin MP Dynamic Grid mp-dynamic-grid-class.php

function add_image_size() {

		if ( function_exists( 'add_image_size' ) ) {

			add_image_size( 'tb-600' , 600 , 450 , true ); // 4x3 ratio

			add_image_size( 'tb-600-masonry' , 600 , 9999 ); // unlimited height

		}

    }

From my functions.php

/*my custom image size*/
add_image_size( 'fixed' , 600 , 450 , false ); // 4x3 ratio

/*Creating Fixed Size Grid*/
add_action( 'init' , 'mpdg_fixed_size_grid' );

function mpdg_fixed_size_grid () {

    global $mpdg;

    if ( class_exists('MPDG') )
        add_filter( $mpdg->hook_prefix . 'product_image_size' , 'mpdg_fixed_size_grid_image_size' , 15 , 2 );

}

function mpdg_fixed_size_grid_image_size( $imagesize = 'fixed' , $instance = array() ) {
    return 'tb-600';
}