Apply sale place for non apply quantities while enabled discount apply from regular price.

Apply sale prices for non-applicable quantities when discounts apply from regular prices.

add_filter('advanced_woo_discount_rules_discount_prices_of_product', function ($discount_prices, $product, $quantity, $cart_item){
    $regular_price = $product->get_regular_price();
    $sale_price = $product->get_price();
    $default_discount = $regular_price - $sale_price;
    $non_applied_qty = $discount_prices['discount_lines']['non_applied']['quantity'];
    if(($default_discount) > 0 && $non_applied_qty > 0){
        $discount_prices['initial_price'] = $sale_price;
        $discount_prices['discounted_price'] = $discount_prices['discounted_price'] - (($default_discount*$non_applied_qty)/$quantity);
    }

    return $discount_prices;
}, 10, 4);

add_filter('advanced_woo_discount_rules_cart_strikeout_price_html', function ($new_item_price_html, $item_price, $cart_item, $cart_item_key){
    $regular_price = $cart_item['data']->get_regular_price();
    $new_item_price_html = preg_replace("/<del>(.*?)<\/del>/s", "<del>".wc_price($regular_price)."</del>", $new_item_price_html);
    return $new_item_price_html;
}, 10, 4);