Actually I think I might understand this - (helped also by looking back at other posts).
The key phrase is that the 25% bonus is based on "miles flown" with BD and all *A and other partners. Hotels, referral bonuses etc. not included.
For "miles flown" we need to substitute "base miles" (i.e. applying the minimum 600 / 800 mile limit)
So my May totals for miles flown were
UA 1686
BD 4414
Total 6100
Bonus@25% = 1525
What was throwing it off was the fact that there was a "full economy" UK internal in there - "miles flown" the minimum 600, but earning 900 miles.
So the sums seem to work.
Except for the fact that I had another late-posting UK internal, which is currently sitting at zero but will go to 900 "once the data process has run".
I'll be interested to see if the system twigs that this flight hasn't been counted for the bonus, and if it will add on another 150 (25% * 600) automatically.
[This message has been edited by grayst (edited 06-16-2003).]