Reverse.ahfI kind of touched on that in the film synopsis. One key point on exiting that barrel roll is to start spraying immedately. The enemy plane needs encouraged to start turning asap. Even if they manage to distance to 600-800 and then start a hard turn, your own pursuit turn will be less drastic due to the distance. That puts the enemy plane in a position of sheding E more rapidly than you.
You might notice that even on the first attempt at a merge, I was positioning for the exact same situation, but he chose not to merge that time.
In that particular situation, I dont think he was gentel enough (ie- shed too much E) in going verticle to escape serious or fatal damage before getting "over the top" on me. In general though I would have tried to get inside his level flight recovery altitude as outlined in
Attack/Pursuit Modes or if I judged the speed difference to be too great, I would have completely dropped pursuit and dive to reposition. Likely I would have seen the latter situation long before it was too late to disengage.
That barrel roll is actually a variation of a maneuver outlined in
Attack/Pursuit Part 2, there it starts as a pursuit, in the film it starts as a merge