Hey Greig,
Welcome back! Try adding the following snippet to the bottom of your theme’s functions.php file and let me know if it works. Please note, it doesn’t address any CSS.
function calendar_mobile_month_img_size( $data ) {
if ( ! isset( $data['eventId'] ) ) return $data;
if ( has_post_thumbnail( $data['eventId'] ) ) {
$image_arr = wp_get_attachment_image_src( get_post_thumbnail_id( $data['eventId'] ), 'full' );
$data['imageSrc'] = $image_arr[ 0 ];
}
return $data;
}
add_filter( 'tribe_events_template_data_array', 'calendar_mobile_month_img_size' );