Does Iron Guard's Glare stack with itself?

Question

The Devoted Spirit Stance Iron Guard Glare reads:

While you are in this stance, any opponent that you threaten takes a -4 penalty on attack rolls against your allies. Tome of Blades p. 59

Let's consider a phalanx of Crusaders with normal melee weapons in the first line and reach weapons in the second line, all in Iron Guard Glare stance. Now an opponent is directly in front of the first line: He attacks the Crusader directly in front of him. He is threatened by the two Crusaders left and right of his target and three Crusaders in the second line, totalling 5, all glaring him down.

Does he get -20 on the attack roll or -4?

Answer 1

Iron Guard's Glare does not stack with itself, the attacker receives a -4 penalty at most.

This falls under the general rule of stacking:

In most cases, modifiers to a given check or roll stack (combine for a cumulative effect) if they come from different sources and have different types (or no type at all), but do not stack if they have the same type or come from the same source (such as the same spell cast twice in succession).

Each of the Crusaders is using the same stance to inflict the penalty, so the penalty does not stack due to the "same source" clause.

It is still not completely useless (at least mechanically) for Crusaders with Iron Guard's Glare to team up, as the stance does not protect the character actually using it. Two or more Crusaders can glare down each others' opponents to not leave gaps in the defense.