Yes - It is clear that if you have full cover you have to use blind fire or fire with an imaging device and opponents get -6 to hit you etc.
However, just standing behind cover does not give you a bonus
(and you are not harder to hit since in SR5 size of the target area doesn't matter unless it is 100 covered - in which case you get -6 because you have to blind fire).
but consider this: standing behind cover and then use the
Take Cover action give you a defensive bonus.
The Take Cover action might very well mean that you "hunker down" behind the cover.
- that to get the positive dice pool bonus you have to do everything you can to cover your most vital areas (like your head and torso)
....while some other parts of your body (like your legs and shoulders) might still stick out depending on the size of whatever you are taking cover behind; giving you full, good or only partial cover bonus.
and if you wish to fire out of the cover while still remaining in cover you use an imaging device or possible even blind fire
...the alternative could be to stick your head out from cover (but that could also mean you are no longer hunkering down behind the cover)
you can also just spend a simple action to take a shot and then the second simple action to duck down behind cover again...
taking cover might also mean that you just kneel behind cover and still have your upper torso and head fully visible (but if that would be the case then you would automatically get that bonus if you passively happen to walk behind a cover that would protect all but your upper torso and head -- but you don't).
Consider this scenario: You are standing behind something that cover your upper torso, head, arms and weapon.
Opponents does not get any negative dice pool modifier
You don't get any positive defense dice pool modifier.
You don't get any negative attack dice pool modifier.
Then you Take Cover. What does that mean...

I think it mean you kneel behind cover and either A) lift your arm and your weapon above the edge so you can still fire back.
Opponents does not get any negative dice pool modifier (because they see your hand and weapon)
You get a positive dice pool modifier of 4 dice because you have good cover and can see your opponent through the live camera feed of your weapon.
You get negative dice pool modifier of 3 dice because you fire with an imaging device.
or B) stay fully hidden
Opponents get a negative dice pool modifier of 6 dice because of blind fire
You don't see your opponent so now you only roll 4 dice as a pool of its own
(can't roll reaction + intuition since if you can't see your attacker you are unaware of the attack)
The only way you can fire back without exposing yourself and giving up your location behind the cover is by shooting
through the cover with a -6 dice blind fire modifier.
food for though.