Installer error is a definite possibility, since I was the one who did the work (late at night too, I might add). And Cylinder 4 is the one that is tucked away towards the front with that dang hose getting in the way.
They are indeed the new "thick" variety. I'm surprised that the car ran at all with that huge crack. The only noticeable problem with the performance was at low RPM at high load.