I hate to break it to you, but the lost kWs early in the charge cycle are being used by your car. It's burning a lot of the incoming power hearing your battery pack for optimal long term resilience of your batteries.
I'd disagree with the resilience reasoning. It's heating the battery to give faster charging in the 75%+ range. You can plug into a supercharger with a 15 degree battery and still charge way faster than 50kW.
I can turn off the heating by turning on Track Mode before I plug in. I'll get max kW until 75-80+% where it starts to significantly slow down as compared to a non-heated battery (it still heats up somewhat just from the charging). Unless you're charging to ~95%+ it works out quicker with the heating off.
And Jolt chargers .. well heating on those .. I'm just not going to go there!