Header Element Page Hero Background Featured Image Size

Hello good people of GeneratePress!

I'm trying have the Header Element Page Hero Featured Image background use a custom size using the code below. The Header Element is set to display on ALL pages but the home page.

However, after re-generating thumbnails, and viewing the source… the header is using the FULL SIZE featured image, instead of one of my fancy custom featured image sizes.

add_action('after_setup_theme', 'esiteful_features');

function esiteful_features() {
	add_image_size('eBanner', 1500, 500, true);
	add_image_size('eFeature', 840, 290, true);
	add_filter( 'generate_page_header_default_size','tu_set_image_size' );
	add_filter( 'image_size_names_choose', 'my_custom_sizes' );
}

function tu_set_image_size() {
    return 'eBanner';
}

Any ideas or direction would be most appreciated.