Yeah, Chris; as far as is known, Dolby hasn't provided precise details as to the DPLIIz processing for the height speakers. What has been said is that the front channels in 5.1 source material aren't affected and that the side surround channels are processed. It may be that just as DPLII extracts out-of-phase material from the front channels in 2-channel sources and sends it to side surrounds, DPLIIz extracts out-of-phase material in the discrete 5.1 side channels and sends it to the height speakers. The rationale would be that the phase difference in the side channels results from the sound arriving from a different height. Of course, it may be more complex than this.
