Its just a calculation that depends on too many factors: Temperature, driving habits and the like.
IMO, ICE cars have a much better distance to empty calculation......... in all of the hybrids ive had (2017 prius, 2021 corolla and 22 sienna) distance to empty is never exact.
use an app like fuely to track your mpg's.
this will give you a more accurate reading.

 

However, last 2 times i added only $20 at a time,

Any idea what could be causing this?"

This.

 

Your confusing it by not getting a full tank. After driving some distance, it should recalculate and reflect a more accurate reading.

 

I would go with fuel gauge on level ground.

DTE estimates sometimes get wonky. Looks like that's what happened to OP. Fuel gauge still shows about a quarter tank.

I had DTE go crazy on me once like this. There's a software flaw somewhere in there under some strange circumstances.

In my case, trip MPG climbed up from 34MPGs to 51MPG after 3/4 of the tank was used up already! DTE was showing I had a lot more miles to go based on 51MPG trip calculation. It was in-your-face lie but it still felt good for a split second.

For the sake of repeating, when low fuel light comes up, you still have about 3 gallons left. That is enough for 80 to 100 miles. You will have enough to get to next gas station, unless you're in middle of nowhere.

 

Thanks all, What I did is I refueled 1 Galan only, Gauge barely moves, but DTE went up to 97 miles... So basically it shows that the fuel gauge is accurate.