I'm in the process of writing a modding 101 guide.
Click Here.The Jump blockers dont add to each other, but if you put them in strategic places, you can ensure that all jump lines and the areas around them are covered.
You can increase the range of them too.
For enforcing your space or creating a block point, I use 5 hangers with a 6-4 mix of fighters and bombers. And then I will built 20 light carriers with the same mix and station them there. These will stop any recons getting through, and should stop all frigates.
The trick is to have enough firepower at your block point, so that the jump blocker gives them enough time to kill anything that comes through.
If your getting Cruisers jumping in, then you need a decent fleet stationed at the exit point to your planets. Fleets need to intercept, as they are not fast enough to chase. So unless you know the enemies always jump in at a specific point and put your fleet there, put them between the jump line in and the one out you want to protect.
For TEC, I've gone a step further and given the Gauss guns more range and much more grunt. 3 Gauss will now take out a recon before the fighters get to it.

I'm building a mod with this stuff in it if anyone is interested. The details as I build it are in the next thread to the modding guide on my forum.
Edit : The range for the jump blocker is universal. You change it for you, but everyone gets the effect. Just remember that when you jump into a planet that has one.