Calculating shipping in cart with variable product dimensions

I’m trying to do calculations with simple and variable products length, width and height for shipping, but I can’t get it work with variable products. When I var_dump, $dim_weight or $length etc they only display at product-page and there they are correct. With simple products it works like it’s supposed to. How can I get it to work with simple and variable products? This is what I tried last time:

add_filter( 'woocommerce_product_get_weight', 'custom_get_weight_from_dimensions', 10, 2 );
function custom_get_weight_from_dimensions( $weight, $product ) {
    $dim_weight = 0;
    if ( ! is_admin() ) {

        $targetted_shipping_ids  = array( 'myshipping' );

        $chosen_shipping_methods  = (array) WC()->session->get('chosen_shipping_methods');
        $matched_shipping_methods = array_intersect( $chosen_shipping_methods, $targetted_shipping_ids );

        if( ! empty($matched_shipping_methods) ) {

            foreach(WC()->cart->get_cart() as $cart_item) { 

                $qty = $cart_item['quantity'];
                $width = $cart_item['data']->get_width();
                $length = $cart_item['data']->get_length();
                $height = $cart_item['data']->get_height();

                $dim_weight += $width * $length * $height * $qty; 
            }
        }
  }

return isset($dim_weight) && $dim_weight > $weight ? $dim_weight : $weight;
}