Yes, unfortunately it was a necessary change I made a while back when I discovered there was a bug relating to the fuel, and that AI are refuelling even if they don't need to. This affects the fairness against the player - they pit for tyres but they take longer in the pits as they are refuelling, so the player can leapfrog several cars during a pitstop. Also, the AI then weigh more and so become slower than the player later in the race.
Personally I do not want to run with fuel simulation turned off, so I decided to restrict the tank size so that ALL cars take the same amount of time in the pits & behave the same at all stages of a long race.
For complete equality, the player should elect to fill the tank at each pitstop and then they will behave the same as the AI.
If I see that this bug has been fixed then I will remove this in a future update, but for now it still seems to be the same.
BUT - if you really don't want this, then it's easy enough to revert it to default.
You will need to edit each upgrade file in the team folders,
just remove the lines in the upgrade files that relate to tank and pitstops:
Take out ALL of these lines and save each file:
HDV=FuelRange=( 0 , 1 , 95 )
HDV=FuelSetting=95 // initial fuel quantity
HDV=NumPitstopsRange=(0,1,5) // the third digit is the number of stops available to choose i.e. 0,1,2, or 3 so choosing 4=3 stops
HDV=NumPitstopsSetting=2 // how many pitstops shown initially
HDV=Pitstop1Range=(1,1,95)
HDV=Pitstop1Setting=95 // pitstop 1 initial fuel setting
HDV=Pitstop2Range=(0,1,95)
HDV=Pitstop2Setting=95
HDV=Pitstop3Range=(0,1,95)
HDV=Pitstop3Setting=95
HDV=Pitstop4Range=(0,1,95)
HDV=Pitstop4Setting=95
All cars would then revert to default tank size and pit stop settings.