New basic equipment: Weapon Scope (10 Cr)
A weapon scope gives the user a +2 bonus to attacks made outside of 1 range increment, but the user also takes a -2 penalty to attacks made within 1 range increment. Adding or removing a weapon scope from a ranged weapon requires an action, but characters with quick draw can do so as a free action. Only firearms and bows can benefit from a weapon scope. The Distance tech enhancement can also be added to a ranged weapon to increase its range increment.
Tactically, why would anyone stay in cover if they had a melee weapon?
It seems to me that the tactics are being dictated by the nature of the melee weapon wielders weapon, and not by the nature of the gunslingers weapon.
If both combatants are wielding firearms, is there an existing reason why they wouldn't attempt to find cover and attack from range? If both combatants have effective missile weapons, is there some particular rule exclusive to firearms that makes it desirable to close the range? I've not got a lot of experience here, but it seems to me that in prd if you have a bow the optimal responce to a firearm is stay more than one range increment away (thereby negating the firearms one major advantage, touch attack at close range). If you can't stay beyond one range increment, the advantage of cover especially at high level is going to be outweighed by the firearms touch attack regardless of any other changes. So you must either close to melee or else move back. You have no other tactical choice.
If at least one combatant is wielding a melee weapon, won't they attempt to close by the most expedient method? What advantage do they have to stalling, behind cover or not?
In movies covering fire is used when both sides are trading shots from behind cover. Then one guy yells "cover me!" and runs for a better position, while his friend lays down the covering fire. So you want there to be an advantage to the guy moving into the open while people are shooting at him.
Would it work if you declared your buddy the "target" of the overwatch, then got an immediate interrupt attack against anyone that shoots at him, and if you hit them they can't shoot him? Obviously needs some wordsmithing, but does that idea accomplish what you want?