Consistently hitting an arbitrary "80% resources consumed" mark? That's terrible in general, and terrible for your group in particular.
It's terrible in general, because it makes the world a grey, unmemorable, low-agency mess. Remember day 27? Oh, was that the day we ended with 19% resources left? No, that was day 43; day 27 was one of the usual 20% days. Bleh. No, I remember the fight where my "not a Frenzied Berserker" ran out of HP, and PSP, and finally dropped, leaving just one man still standing at the end of what otherwise wouldn't have been a terribly memorable or important fight.
Of course that is boring, but it won't actually happen.
The 80% mark is an average. Dice change. Tactics change. Environments change. Sometimes the DM makes a mistake or forgets to factor something in. And, some encounters are just more (or less) effective against certain party compositions.