It's been my experience, that the further out you look the more expensive it is. If you look for February flights in December, you should see the flights are less expensive.
Airlines practice what is referred to as yield management - trying to achieve optimum revenue from a flight while maintaining a profitable load factor. As such, flights are priced when the airline first allows bookings for that flight - typically 12 months in advance of the departure date. They look at anticipated fuel costs (typically the largest and most volatile of the variable costs), and price the seats so as to achieve an acceptable profit margin with the average historical load factor for that flight. They don't typically adjust the pricing until 3-5 months before departure, and adjust prices then to take into account changes in fuel costs as well as how much of the required load factor they've already booked. If they've already booked more than the required load factor to be profitable, that's an indication of high demand, so they may not cut prices at all, or may even raise prices; if they are behind historical norms in filling up the plane, you might see a "flash sale" that only lasts 1-3 days, just to fill up enough empty seats to get the plane to a better load factor. I benefitted from one of these last year, when a trip to Cozumel in the first week of December, DFW to CZM round trip, had a big drop in price about mid-July - on a Saturday morning the round trip price dropped from $542 to $362. By Sunday P.M., the price was back up to $542. The Airplane will end the sale before completely filling the plane, leaving the last 5%-10% of the plane available for full fare tickets. Then, if the plane is not fully booked, it might offer more low-fare tickets in the last 21 days before departure.
If you need to firmly plan arrival and departure dates for a trip, and it is a popular destination and high season (i.e., Cozumel for the Christmas-New Years week, or Cozumel for Carnival), you might well risk the flight being fully booked at full fare prices as early as 6 months before departure; if you are looking at a more "off-season" trip, there is still some risk of a flight being fully booked, but you might save a lot of money by starting to check prices daily about 4-5 months out, hoping that you can get into a "flash sale", or even waiting until 3 weeks before departure hoping to snare a "last minute" deal. It's all a bit of a roll of the dice, taking the risk of a booked up flight (and no trip) vs. the possibility of potentially big savings.