I went back & forth with Mike a bit yesterday. He's not buying the working theory we have here. His first explanation is that on the cold start mornings, the heater goes into boost mode and boost mode is more susceptible to the fuel cavitation. On warmer mornings, the heater doesn't go into boost mode and can better tolerate the cavitation bubbles in the fuel line. He's trusting the fault codes and still believes that it is a fuel supply issue (cavitation).
So why would the warm air exhaust back pressure affect this? The heater heats up faster and gets out of boost mode.
With our very small sample, we see a correlation of folks with the cold start issue that have no warm air duct and those with ducting not having the issue. He didn't have an explanation for this.
Anyway, I don't know that we'll get to the bottom of this unless someone with the issue gets hooked up to the EasyScan diagnostic tool to watch the sensors in real time. In my case, this was very enlightening.
At least there seems to be a workaround.