Solved

Fuel level replaced not added to.

I recently accidentally pitted the same driver twice in a row, not their teammate. I had to wait in pitlane for the crew to 'add' less fuel than the previous stop.

This, while frustrating, implies I can't start with ss tyres, for quick qually time, and a few quick (for fuel load) laps, before putting harder tyres for a longer stint in a quick stop as not much extra fuel needed to match tyres to bigger fuel load.

Thanks

I think what he meant was that currently the pit times are (roughly) the same no matter how much fuel gets refueled. So tactics like deliberately overfueling the short first (super soft) stint so that for the longer second (hard perhaps) stint only a little bit of fuel needs be added, to achieve a shorter pit stop, isn't possible right now. OK, that description is not any less confusing I guess but I hope it helps.

Something the devs are thinking over and might be added later in time.
Is the ability to do a splash and dash, refuel the car only and not change tyres and change tyres only and not refuel. currently can do tyre changes only in changeable weather conditions. Handy if you pitted and 2 laps later it rains, empty the fuel load to zero and fit inters only. it's not any quicker at the moment but if they add it in later as a feature, it could allow faster stops.

I also suggested wing adjustments
+1 if it starts raining
-1 if it stops raining.

it was in the same post as the splash'n'dash suggestion, not sure if it was included in the we will think about it