Shouldn't make much of a difference living on a hill. Because what goes up must comes down.
I've got a 5,000ft hill near me, It takes about 30 minutes to climb and the card would show 999 Wh/mi.
But on the wat down it shows -999 Wh/mi. And from ground level on one side to the other side is pretty much the same as if I had driven a straight line.
Look at the Energy Graph and see what it is telling you the reason for the low performance is. What is the average speed that you drive?