Why are shipping rates so high on my account?

I'm attempting to a build an integration of EasyShip into a new marketplace. For some reason the rates calculator is always returning a total cost much higher then my client would expect to pay.

These are the sort of rates I was hoping to get returned:

https://www.easyship.com/en-gb/shipping-rate-calculator/unitedkingdom-to-germany?weight=1&weight_unit=kg&category_slug=sport_leisure&width=11&height=6&length=16&dimension_unit=in&range=%3C100

However, using the rates API, I get £46 returned. See below:

Sender Address: Kamminer Str. 24 Berlin 10589 Germany - Paul
Ship To Country: United Kingdom
Category/HS Code: Sport & Leisure
Box Name: Custom Box
Box Dimensions: 20 x 20 x 20 cm Weight: 1 kg
Currency: GBP

Is there a setting that could be causing this difference?