It's a little more complicated then that. Think about it this way. The forward curve has a propensity to trade at a discount because there is a steep economic cost for the producer to store gas. The cost is implicit, not explicit. Meaning it's not an actual dollar figure per day that is his concern. Producers make money by actually "selling" their gas. Not trading it. They make money moving MMbtus. If you are still with me now, keep following...they would rather sell their forward gas below fair value because they get paid on volume more so then on price. So they exert downward pressure on the forward curve in certain spots. Since the forward curve trades pretty flat the price of the spread acts like an option. As you move forward in time, the curve is not acting like a storage market, it starts behaving like a delivery market. As you get closer to the delivery cycle the gas becomes more sensitive to supply constraints and the pricing structure changes. The sensitivity to backwardation becomes very high. Think of this gamma on an option. And the backwardation itself as the delta. Now think of the supply constraint as implied volatility on an option. Now in the equity world, you would have to pay for this right to own the convexity. However, the market in this case is actually paying you for it, hence the "free embedded option". Let me know if this is making sense to you.
nicely done
