There are two distinct issues. One is range and the other is energy efficiency. When considering range only the distance traveled needs to be considered. When considering efficiency, the energy used to preheat the battery and cabin should be considered. I read a new term while reading some of the papers on this, "recharge allocation factor" This is the ratio of the energy drawn from the AC supply compared to the DC energy drawn from the battery. This is intended to be a metric of the battery and charging equipment, but in real world it should also include all other energy draw including vampire drain.