BEagle - nice one. Now I put on the "devils advocate" hat and say, "Ah, but what if the ACTUAL drift at altitude is only, say, three degrees - but the MAX drift at that altitude is as much as eight degrees."
You lay off 3 x 8° (24°) outbound in the hold - when it should only be 9°. What will that do to the inbound?
(rustle: darned good point, sir!! That's what comes of posting before your second cup of coffee in the morning. I've done it for you now).