Attacker Firing From Cover, and Multiple Targets questions Options

[Ranger]

When do these two modifiers apply?

Does Attacker Firing From Cover apply whenever you are behind *any* kind of cover? For example, if you are standing behind a wall that comes up to your waist and thus does not impair your visibility in any way, does you suffer this penalty? Or, does Attacker Firing From Cover only apply if you are completely hidden behind cover?

For the Multiple Targets modifier, do you suffer the -2 when attacking both the first and the second target, or do you suffer -2 only when attacking the second target?

Similarly, when using a full burst to attack two or three targets, do you suffer a penalty, such as -2 against two targets, and -4 against three? -2 against two or three? No penalty at all?