I have been tracking flights (for 1 airline in particular but sometimes comparing with others to verify) for about the last 10 months. The best prices were about 6 months out, yet around 6-12 weeks from the departure date, the same flights were only about $7 higher. In between, they would fluctuate and sometimes, quite a bit. Holidays threw it out of whack, unless purchased early, and being flexible about dates. (Disclaimer - these are my notes for a specific time period, and may not correlate with future airline published pricing policies.)

Rare events that occured during the tracked time period - Jamaica-collected taxes (departures) increased - and some US-collected taxes (departures) expired until they were re-instated by the US. I forget which order these happened, but I think there was some overlap - before the increase and while expired, during which a ticket could have been purchased at the lowest overall COST.