Rodham - another very interesting post, thank you for the graphs.
It may help increase battery temperature if you timed the charge to finish just before preconditioning started - you would then have the residual warmth from the battery charge as a start point for the pre-con. Precon heater is only 1kW and the battery pack can't absorb too much heat in one go - as your graphs show it takes energy then lets it dissipate through the pack before taking more energy.
Do you know what the battery temperature was at the end of charging?
2015 i3 ReX Solar Orange, Loft interior world. BMW professional, 19" turbine-spoke 429 wheels, DC rapid charging, driving assistant plus.