It actually might make sense to have different types of blockades that you could choose to enforce.
A close/loose blockade would require less superiority and give less tension with neutrals, but on the flip side be easier to break as they could not avoid battle without giving up the blockade. Also would drag the blockading force into range of land based aircraft.
A distant blockade would require a lot more superiority and give more tension, but be much harder to break because you can't bring a large part of the force to battle at once. Have to break it up a few cruisers at a time.
I cannot see sence. If you have distant blockade, you need force to patrol blockade area and some ships which can regularly replace ships on patrol. Than you need support force that can deal with any force that will try to break blockade or have another strategy. This means only some ships are at sea.
In close blockade you need force which is superior to port/ports you blockade. You need force to regularly replace such patrolling force. It was possible in age of sail when you need to replenish only supplies but when your force is coal dependent they need regularly go back to port. So your force need to be quite superior, your main force will be doing blockade. Not mention that your enemy can choose time of action, use light forces etc. It is much more risky and it gives no advantage except early warning.
The more I think about this the more I understand why the blockade mechanism is the way it is. Every blockade is a special circumstance. Russia blockading Germany is a completely different prospect than the other way around or another country blockading either one. A close blockade that makes perfect sense in 1903 could be perfectly suicidal in 1933. A person could spend massive amounts of time trying to perfect it and add very little value to the gameplay.
I'd like to see some tweaks, but it definitely doesn't deserve to be top of the priority list.