Revenue management is always going to be a complex and to the outsider ie customers an unpredictable thing. I would be surprised if BA ever went the way of alot of the US airlines by releasing all seat for miles near to flight just would not make economic sense, last minute all more profitable.

If there was a statistical analysis of when miles booking were made I would suggest it would be a long long long time ahead of money bookings. I have just changed my plan from being in UK to now going abroad for Xmas. I thought I would look and we found some lucky avail - but three months out I was not hopefully (and not just because of holiday season).

That said I had a last minute personal trip to Scotland to make and I was being quotes the full fare, and to my surprise I was offered a miles booking when I checked (even better I ended up spendign only 4.5K miles as I could use a cash combination).

Maybe a little survey what was the time ahead of flying you booked your last miles flight?