Calculation not properly calculated by 2 products

Hi i have set the follwing settings
24|5.74|1|
18|21.95|2|
18|21.95|3|
18|40.95|4|

someone from germany buy to products from 18kg each and he still needs to pay one time shippingcost.

How can i solve this problem?

https://www.ads-software.com/plugins/oik-weightcountry-shipping/