Probably you should include prices with VAT and use the tax field for fixed amount, because you have 2 variables, one for the EU zone, and one for 4eur fixed per products.

It should work like this:
{instantpaypal}action=addtocart,price=30,taxamount=12.50,taxtext=Fixed shipping+,productname=DemoProductxxx1,showquantity=1,shippingamount=4,shippingtext=Shipping per item,shippingtype=multiple{/instantpaypal}

You can switch between shippingtype=multiple or shippingtype=single to apply to single items

Best regards


John