Carrier shipping incorrectly identifying items as overweight.

Site URL: https://icamanufacturingtest.squarespace.com/

My client has had an online store for a few years now. Typically we sell a lot of smaller items, but we offer much larger ones. We use Fed Ex or UPS for these larger products. Setting up the shipping on our new Squarespace store, I can't have the product size above 24x24x20. It's telling me its oversized. I regularly ship 30x30x20 100lb orders, and have never had an issue with it. Is there some way I can override this feature and still utilize the carrier calculated function? We sell over 900 different products ranging from .001oz capacitors, to 120 lb power supplies. As we ship to the entire USA, we can't just set a flat rate for everything. I've already set up the custom boxes for each carrier. "With FedEx Express® U.S. services, you can ship packages up to 150 lbs.; up to 119" in length and 165" in length and girth." Directly from FedEx. Has anybody else encountered this problem? More importantly is there a way to tell the website my products aren't overweight, allowing me to accurately calculate shipping cost?