Permanent address affects whether VAT is payable or not. Sites are expected to hold at least 2 forms of location proof, and factor these together to decide what VAT rate to charge. 2 forms should ideally match up. If they don't directives say to collect more proof until 2 of them match up. Sites and the software will typically just let it slide and go with any 1. One of these forms of proof is typically a billing address. If there is a mismatch (billing address and IP), well, it's up to the site as to which rate they charge.
Technically speaking, if a site is relying on IP location to charge VAT, automatic payments will not include VAT (although you should technically be paying it, the burden falls upon the seller to ensure this. afaik, it's not your responsibility).