Update:
Past two tanks of gas have been the worst I've had since getting the car, at ~54 and ~55. The weather has been a bit cooler, but more importantly they were 100% city driving, with a vast majority being my wife's commute. Something seems to have changed in her driving habits. I've seen the gauge with numbers as low as 35 after her commute, and she generally leaves me with 2-3 bars of battery. She is not an aggressive driver, and I know she doesn't rev it up. I suspect she is actually keeping the RPM too low and leaning heavily on assist. To support that there isn't anything wrong with the car, I'm still getting 60+ around town in traffic.
I modified the lower grille block a bit, using foam to make it easily adjustable, and keeping unused pieces in the hatch. I'd estimate that even with all four foam pieces in place perhaps 20% is still open along the top, so with three on it should be approximately 60% blocked. On particularly cold days I'll drive around with an 80% block and keep an eye on temps, but I suspect it'll be fine.
