I am based in NYC. My strategy is to book MC very early on, maybe 6 months out or more. I check fares through refare-ing daily (change flights option on the itinerary page). I try refare-ing each leg and then round trip. This strategy has worked for me quite well. For example, I booked JFK-MAD r/t in MC for mid-May. Total fare in D1 was $3300 after refare-ing. I see that for this time of year, these flights can go for $6000+ in D1.

I have a trip next month, one way to Bilbao and the return from Athens. I initially booked in MC in January and gradually refared to D1 over the past few months. I was at about $4,700 r/t in D1, but then I got a magical $800 eCredit because I checked the fares every day.

This requires time and planning, but it works. Good luck and I hope this helps.