Why does BC pick VAT Prod. Posting Group from GL Account Card for Prepayment Invoice?

If I am posting a Purchase Prepayment Invoice, and do not have a VAT Prod. Posting Group on my Advance to Supplier GL Account Card, I get no VAT Line in GL Entry during Prepayment Invoice Preview posting. Even the VAT Entry has a line with 0 VAT Amount.

But if I have a VAT Prod. Posting Group in GL Account Card, I do get the VAT.

Why does for the Purchase Prepayment Invoice the VAT Prod. Posting Group not taken from Line but is taken from GL Account Card. I cannot have it on GL Account Card as we can have different VAT Prod. Posting group on line during Prepayment Invoice and it won’t work.

Thank you in advance for the guidance.