Thanks for working that out for me .Living in Wales there are plenty of elevation changes , more so on the trip back so that accounts for part of the difference . Traffic was also much heavier . When I picked up my Ioniq I travelled along the same route and achieved 64.5 with only myself in the car so there is an improvement . Maybe the engine bedding in or maybe I'm just driving better . In any case ,I can live with 69 mpg fully laden and the unladen trip shows you can get near the 83.1 mpg claimed . In fact the first 7 miles the gauge was showing 99.9 mpg . I thought it was broken until I got up to motorway speedsTo average 75 mpg after the first half of trip at 81, your return leg was around 69 mpg. That is a 17% dip between trip legs. How much do you consider monumental? This is without correcting for wind, temperature, or elevation changes of course which could change your results, but I'd consider a 17% difference significant. That is more than the difference between summer and winter driving.