How can I disable combined shipping fees on large items?

[sneakerglass]

I have these large shoebox sized boxes that I sell to customers and the shipping is quite expensive. When someone buys more than 1 though, Shopify charges full shipping for the first item but then a greatly reduced price for each subsequent box. I am losing a lot of money on shipping because I have to pay full price on each box as they are all too big to combine into one box. 

How do i prevent this from happening and force shopify to charge the full shipping price on each box?

[Anindita]

Hi @sneakerglass 

I feel the best way to solve this will be using your custom boxes. You can set the weight & dimensions of the box based on your product/s size. To set your Custom boxes you can check out PH MultiCarrier Shipping Label . The app allows you to use both carrier boxes & custom boxes based on your requirement. Attaching one image for a better understanding.

Let me know if you have any queries. I will be happy to help!