It can be frustrating when your instrumentation makes you think you have a good tank on the way and then it disappoints - kind of like growing carrots with healthy, tall tops only to find the actual edible bit is tiny
Given the bad conditions and tyres and the size of car I would say that figure is not bad. If you look at your fuel log though
you can see that your average won't be affected too much by one bad tank.
Sometimes taking a break helps, maybe do a tank with no hypermiling and see what the effect on FE is - then work out the cost and then start again
