[Typo3-shop] shipping.2.priceTax once per product

[redacted name]

Hello,

I have this setting in Ts:

plugin.tt_products.shipping.2.priceTax = 15.00

I would like to charge the shipping price once per product, but with 
this setting its only charged once for all products in the basket.
There is also the setting 'percentOfGoodstotal' which charges on 
percent-basis, but I would rather like to charge a fix sum per product.

Is there a setting I oversaw, or should I modify the code?

Thank you all, Tim