Threatened squares with 10-ft. reach (2 squares or 10 ft?)

[Bihlbo]

From the searching I've done in the Pathfinder materials, weapons with the "reach" quality (except the whip) double the wielder's natural reach. So a Medium humanoid's reach with that weapon is everything 10 feet away, and of course not the squares adjacent.

The question we've run into is how you determine where 10 feet from you lies. The first square diagonal from you is 5' but the next is 15', using the normal method of determining distance. So that means the corners are clipped off of what would otherwise be a 5 square-wide ring around your character.

However, under "Big and Little Creatures in Combat" in the D&D 3.5 DMG on page 29, in the Natural Reach portion it says the following:

DMG wrote:

The exception is a creature with 10-foot reach. It threatens targets up to 2 squares away, including a 2-square distance diagonally away from its square.

I haven't found the same exception in Pathfinder rules, which leads me to believe that it was either intended but not included as an oversight, or we are supposed to use the normal distance rules to determine reach, even with this narrow and problematic distance of 10 feet.

Who can help me find an official rule that answers this question?

[StabbittyDoom]

Either a weapon is sometimes 15ft reach and sometimes 10ft reach, or you leave a corner that doesn't threaten an opponent who approaches for no game-world reason. I think the official answer is the latter.

My Solution:

If an opponent crosses a diagonal between two threatened squares and doesn't 5-ft step, they can provoke an AoO. Outside of this, that square is not threatened.

XO
OX

If you started at the upper-left X, and O was the threatened area from the reach weapon, going down-right would trigger an AoO unless you used a 5-ft step or used acrobatics. If you stay in that square and cast or use a ranged weapon, you are safe as it isn't threatened.

[DM_Blake]

3.5 and Pathfinder seem to handle this differently.

There was a big thread on this a while back, I'll see if I can find it.

Here it is right here.

It even has an official dev response explaining why the corners are missing, and then since people brought up the 3.5 rule, there is a followup official response about the fact that that is a different game.