Why can not expect total compensation for a price decline when futures prices are below spot prices

The dollar gain per barrel of oil from the short futures contracts is: (68.2067.40)+(67.0066.50)+(66.3065.90)=1.70 The oil price declined from USD 69 to USD 66 . Receiving only USD 1.70 per barrel compensation for a price decline of USD 3.00 may appear unsatisfactory. However, we cannot expect total compensation for a price decline when futures prices are below spot prices. The best we