Ajeh, thanks for the reply but I think the problem is misunderstood.

Adjusting max shipping weight or tare has no effect on the shipping cost when it is used with the FedEx module. I tested with the shopping cart and it is not splitting the order into separate boxes when it should. Playing with the max weight or tare has no effect.

The tare option talks about small sizes and large sizes. What's the difference between large and small? This is not defined anywhere. Was Zen Cart written by programmers who hate math? I don't understand how this ecommerce system can work without correct calculations and without defining values and just using vague words like "large" and "small."