There might be layering tutorials around but none I know of are related to subframe, so ehrm. You might have missed this, but if you layer more than 5 particles, you get blackholes. You can layer 1000 or so particles if you create the stack above EHOLE (a type of wall), but that's ugly.
I dunno why my comment is gone, but what he said.
Flipped version isn't work because if you flip it, you ruin the order of particles: CONV is placed before ARAY.