It's meant like that. Shipping per product since we are not linking directly to a shipper to calculate shipping. Also since we are not handling shipping ourselves, we pay a standard fee to vendors at Aliexpress.
If you just want a flat shipping... I don't think the plugin can do it. At least I haven't figure out how. I just offer free shipping on all products and charge shipping on some promo items with extremely good prices.
Another way is to create a combo units variation. When you are adding a product, in the variation tab you can create "new" variations which could be 2 units, 3 units, 5 units, 10 units etc with discounts for more items (of the same) purchased together. This way, you can charge one shipping, offer a discount, and sell more. Or you can just switch to WooCommerce version and I'm sure you'll find some interesting plugins to handle that.