Brayshaw, I have played around with this quite a bit and have figured out that it comes down to just a few things. Some may disagree but I have done experiments strictly to see the effects.
I have used many different recipes, flours,ingredients,mix methods, fermentation times and bake temperatures, and it seems a few things hold true.
1) A properly fermented dough. What I mean by this is make sure your dough has been fermented long enough. With your yeast% I would probably drag that out to at 2-3 days, pending your fridge temps.
2) Letting your dough come up to a good temp before using. I dont have a set temp or time but usually its around 3 hours. You should see the dough start to rise. This gets the yeast active again and produces that good gas that you want in the dough.
3) Handling technique. Ball your dough before you put it in the fridge and DO NOT re-knead the dough before shaping the skin. This mangles the developed dough structure and will ruin the texture that you are looking for.
I will pull a quote from another post I made on the subject.
"First the time in which you let the dough warm up can have a large effect on the finished crust.
When you start to form the skin if you just start pressing it flat you will evenly distribute the gasses through the skin. If you start working the very center of the ball first and work from the center out you force all the built up gasses to the outer edges, which become the rim. Once you can get all that gas evenly to the rim your golden. Just add the hot stone.
I work from the center out pressing lightly with my knuckles until I can get it big enough to fly it a bit. But what I dont do is disturb the rim... at all.
If a person uses a rolling pin you will get a flatter less puffy rim.
The same with lower/higher temps. In my opinion you are fighting the time it takes for the very outside skin of the rim to become hard/crusty and non-elastic with how fast you heat up the gasses inside the skin.
The faster you can heat up those gasses, the faster they will expand. If they expand faster than the skin of the crust can solidify you will get a bubble or a pocket.
If you can heat up the gasses really fast you get alot of expansion before the outside can solidify and you get nice big holes.
At least thats my theory for now. Either way it seems to work for me."
4) A screamin hot stone that is properly pre-heated. At 240C your stone is not near hot enough to attain the results your looking for. I have done tests with the same exact dough and only changed the oven temps. The results are eye opening, in a home environment "the hotter the better". Crank that oven up all the way and pay close attention. You will see a difference.
Do these things and you will see a good improvement in the "airiness" of your crusts. Try it out and report your results. This of course is just my opinion, but it works for me.