I have read many of your PHEV
I have read many of your PHEV articles and agree with many of your conclusions. One question I have is how do you determine that your "lifetime miles per kWh figure is about 3.2" for your Sorento PHEV? 3.2 mi/kWh is equivalent to 108 MPGe, which is 36% higher than the EPA rating of 79 MPGe for your Sorento PHEV. I am an engineer by training and tend to be skeptical when there is a discrepancy this large. EPA ratings usually overpredict real-world experience, not underpredict it.
I have owned a Ford Escape PHEV for more than a year. I have kept a complete log of my miles driven, gas purchases, and charging sessions including kWh measured at the wall outlet with a "Kill-a-Watt" brand meter. At the end of the first year, I calculated/estimated the performance of my car after 9,840 miles and found that I drove about 70% on plug-in electricity (2299 kWh used) and 30% in gas/hybrid mode (79.4 gal used). With plug-in electricity, I achieved about 101 MPGe (3.0 mi/kWh), which is just under the EPA rating of 105 MPGe for my Escape. In gas/hybrid mode, I achieved about 37 MPG, which is just under the EPA rating of 40 MPG. Note that I live in Tennessee with mild winters and my car is parked in a garage and doesn't have power-hungry accessories such as heated seats/wheel. I am sure my performance would have been worse if I lived further north with longer, colder winters.
Based upon my data and experience, I find it suspicious that you claim to be 36% more efficient in plug-in electric mode than the EPA rating for your car. While that type of performance may be possible for brief periods under optimum weather and driving conditions, I think it would be nearly impossible to sustain as a long-term average.