I use the rule if I am about to black he has already done so. Most "NEW" pilots will try to pull lead and get a shot under the nose.
But as Puma has pointed out,some pilots will not do this! Instead they may change pursuit from lead to a lag and have reserve energy to attack.
Also what if the pilot doesnt follow? You will have given up alt and the enemy can still be in a position to attack.
Combat is just too fluid to say do this or do that and the enemy will do this or that. If it worked that way it wouldnt take as long as it does to become proficient at aerial combat.