Does reach let you threaten an opponent if there is another opponent between you?

Question

Okay, the following situation came up in a recent game of Pathfinder. Pretend the following are in a straight line, in a standard 5' grid with their bases touching each other.

player's summoned creature with 10' reach -> enemy minion-> enemy boss -> player

The only creature with extra reach in this scenario is the summoned creature. Does it threaten the enemy boss (who is 10' away) and provide flanking for the player?

The rules state "You threaten all squares into which you can make a melee attack", which led my group to think it did indeed threaten the enemy boss. However, we're unclear on if the enemy minion between the boss and summoned creature provides cover, and if so, how that might impact threatened squares.

Answer 1

You would flank, but cannot make Attacks of Opportunity*

Threatening

Threatened Squares: You threaten all squares into which you can make a melee attack, even when it is not your turn. Generally, that means everything in all squares adjacent to your space (including diagonally). An enemy that takes certain actions while in a threatened square provokes an attack of opportunity from you. If you're unarmed, you don't normally threaten any squares and thus can't make attacks of opportunity.

AoO Rule:

Cover and Attacks of Opportunity: You can't execute an attack of opportunity against an opponent with cover relative to you.

Soft Cover Rule:

Soft Cover: Creatures, even your enemies, can provide you with cover against ranged attacks, giving you a +4 bonus to AC. However, such soft cover provides no bonus on Reflex saves, nor does soft cover allow you to make a Stealth check.

Those both come from the PRD section on Combat

As @Jim Kiley notes, there is no rule that states cover negates threatening. Just that it negates taking AoOs.

So, yes, the creature would provide a flanking bonus, but would be unable to make attacks of opportunity.

*This is muddied a bit by the fact that "Threatened Squares" are only described under attacks of opportunity, and it is a bit unclear if "threaten" == "can make an AoO". RAW, they're not technically the same thing, and thus my interpretation.

Edit: Turns out Creatures are only cover against ranged attacks, (double edit) but you determine cover as if with range if the target is not adjacent.

When making a melee attack against a target that isn't adjacent to you (such as with a reach weapon), use the rules for determining cover from ranged attacks.

BUT

If the creature is large or larger, it gets to do this (which means if it's hampered by a medium creature it could probably finagle itself outside of cover):

Big Creatures and Cover: Any creature with a space larger than 5 feet (1 square) determines cover against melee attacks slightly differently than smaller creatures do. Such a creature can choose any square that it occupies to determine if an opponent has cover against its melee attacks. Similarly, when making a melee attack against such a creature, you can pick any of the squares it occupies to determine if it has cover against you.

Answer 2

As you have -- and per the PF SRD (http://www.d20pfsrd.com/gamemastering/combat#TOC-Threatened-Squares), "You threaten all squares into which you can make a melee attack". Having an additional character between two opponents provides cover to both, but there's no mention in the rules that cover negates threatening, so flanking is still valid. In the PF SRD there's an example of an ogre providing flanking despite not being adjacent to the target he threatens.