ops v heads

Have been observing the margin b/w the ops and the heads. A month or so ago the difference was 2.2 cents. Now the variation is a full four cents. I appreciate that the value of the ops diminishes as the time moves closer to expiry and they are still out of the money, but I wouldn't have thought that the difference would be so great.
Does it mean that the heads are overvalued or that the ops are undervalued? Or is this the correct correlation at this stage of the game?
Any thoughts from more experienced followers appreciated.