This helped my design, but did not correct the problem, only delayed it. After some time (100 or so blaze) I ended up with 6 blaze floating (bobbing) and not triggering the pressure plates. If I kill them it will work again for a bit. Better than adding a 3rd ring of pistons putting the cone at around 60, somebody else made a better suggestion to simply fill in the walls. While this may lower your spawn rate a bit by giving less area to spawn, it will more than make up for that in the fact that it will work for a while (before needing to kill the floaters) and cost (virtually) nothing.
Actually you have to put a new ring of pistons on the top layer AND add pistons on the corners on all floors (12 corners), if your using Etho's original design, this will render the lava on/off switch unusable. As an alternative, you can only put pistons on the corners of the upper 2 rings, leaving the four corners of the lower ring without pistons, so far that haven't stopped the blazes for me, but they do keep stuck on those corners, luckily only 4, so the spawner does not stop. With this the lave on/off still works, but it's much slower, since the lava now takes several minutes to disappear. I'm working on a system to avoid this, but so far no good answer.
