Generally, it's always best to book as early as possible IMO. Prices increase as space gets limited. There may be discounts offered nearer the flight if they are not filling seats, but it's a gamble.
However, in my experience, it's still very variable. I look at prices approaching the dates I'm looking for too, but this is actually no indication of what the actual prices will be once your dates are available. They can be completely different, and they also very from day to day.
Once, I was looking at two dates, either the Tuesday or the Wednesday in one particular week. The Wednesday was much cheaper when it was released, but the very next day the prices had swapped.
For what it's worth, in November 2014 I paid £608 (one person) for a VA return economy flight from Manchester to Orlando. I now try to go Premium Economy where possible, and in February 2018 I paid £887. For February 2019, I've paid £916. Depending on the actual days of the week, the same flight can go up to £2000 or more.
This is the dilemma I have that I mentioned in my recent thread about the Magical Express ("Virgin Holidays with WDW hotel - no shuttle?")- you book WDW hotels when they're released, as availability can be limited and they disappear quickly, but you might have up to 6 months to go before flights become available, so you take a chance on what prices you will eventually end up paying for the dates you've booked the hotel for.
For me, BA flights are not practical as they go from Gatwick. They may be cheaper than VA (I don't know, but people seem to say the are) but the added expense of me getting down to Gatwick and probably staying in a hotel overnight there, together with that inconvenience, negates the cheaper cost of the actual flights.
I was in the bubble on the VA flight this February (Premium Economy) and managed to get seats there for my next trip too. I didn't know that BA do seats in the bubble for economy and premium economy, I thought they reserved the bubble for upper/business class. But anyway, yes it was very nice quiet and prvate cabin. If you're going economy, I'd say the front row in the bubble is recommended, huge gap in front of the seats, although I think I'd feel a little "exposed"! With Premium Economy, you get slightly wider seats and more legroom and, if inteh bubble, a storage bin at the window. But they're still cramped, it's not exactly the height of comfort! But if the difference in price is not too outrageous, it's worth it for me.
Anyway, in summary, I don't think there are any instructions that anyone can give you as to when is the best time to buy reasonably-priced tickets, I don't think there is a magic formnual! Still trying to work it all out myself. I'm hopihn to go again in November 2020, so I'm coming up with the same dilemma again now...book the hotel in March/April 2019 when Disney releases the rooms, and gamble on the flight prices when they're released 6 months later, or wait until November 2019 to book the whole thing and risk the cheraper hotel rooms not being available any more.
BTW just a heads-up about Virgin. As I say, I've booked three VA journeys to go to WDW, and twice they have cancelled one of my flights and moved me back or forward a day, meaning in both cases I had to book an extra night at my Disney hotel. The first time it was OK as I could just extend my hotel reservation by one night, the second time my hotel wasn't available for that extra night so had to book at a different hotel, which is awkward. It's really annoying that airlines can do this, even after you've paid in full.
