Hi Laura L,
Oporto is on the mainland, or continent, of Portugal.
The Azores (and Madeira) are autonomous regions of Portugal. Both are archipelagos.
0.6% is pretty darn close to half of 1%. That's not much at all.
For those seeking unknown parentages, they HAVE TO test (or transfer) with all the major DNA testing companies. You don't know where that crucial match will be. Your dad did 23 and Me. He need to also be in Family Tree DNA (or FTDNA), My Heritage, and Ancestry. Those are the major 4 companies he needs to be in. He can directly test with the remaining 3 companies if he wishes. Or he can download his raw data from 23 and Me (link below) and upload it to FTDNA and My Heritage (links below). Ancestry does not allow transfers; one must directly test with them.
Downloading raw data from 23 and Me:
Upload to FTDNA (I suggest you unlock the tools - $19 USD):
Upload to My Heritage
(I suggest you unlock the tools - $29 USD)
Ancestry (it's on sale at the moment for $59 instead of $99. Don't bother with the membership. They have nothing for Portugal or the Azores. Just click the orange "Proceed to Checkout button):
Once you transfer to FTDNA, let me know. There's an Azores DNA Project there and I manage it. I can send you directions on how to join the project. Once your dad is in, I can view his page and give you a better idea of where to look.
Researching: São Miguel island: Vila Franca, Ponta Garca, Ribeira Quente, Ribeira das Tainhas, Achada