Close-fitting and armor

[Woodclaw]

I was reviewing some of the armour basics the other day and I got a question about how Close-fitting works.

This is the RAW

The selected item’s Protection rating gets a bonus of +1.
This upgrade may be applied to any suit of armour or helm, and can be selected multiple times (always up to a maximum of three Qualities per item).

Very straightforward apparently, but a question poped up in my head: since armours Protection is listed in dices how does it apply? Is it a straight bonus to the final result or an extra dice?
A Leather Corslet with Close-fitting 1 would provide 3d or 2d+1.

Can anyone help me on this?

[Yusei]

Just a straight +1 bonus, not an extra dice.