I was assuming it was, for each tile between you and the target, it adds 1 + 10% of base ranged defense to your final ranged defense. That’s what the description seems to say.
So at 5 tiles, 10 base ranged defense, you’d have +10 to your ranged defense. At 8 tiles, 20 based ranged defense, you’d have +24 to your ranged defense.
Someone has told me this is very wrong, and that the benefit is actually much less than that.
It’s what you suggested above, and the “base ranged defence” doesn’t include any bonuses from shields, Dodge, confident morale or the Short trait. At least that’s what I understand/assume. Unfortunately, many of the perk bonuses aren’t very tangible in-game, so that it’s difficult to judge their worth. With Dodge you get a nice icon displaying how much bonus is currently in operation. Obviously, with Anticipation, the bonus is specific to the enemy attacking you and the position from which the attack takes place, so that there’s no static bonus that can be displayed when it’s the character’s turn.