I wouldn't chop your throttle in that situation, you want to keep a hold of as much E as you can so you can use it later for following up or bugging out.
What you are trying to do is firstly, deny your attacker a easy shot/kill; secondly manoeuvre as efficiently as possible (eg do the minimum required to get the result you're after); thirdly, and by no means least important, attempt to generate a situation where you become the aggressor (if even for a short period of time - eg a brief snapshot. Or even turn the tables completely).
Ideally, you want to do something which encompasses all your tactical goals in one. One such move is the barrel-roll defence - which is out of scope of this thread.
The first, and simplest, of our tactical goals is "deny the easy shot". For someone new this is first thing they will learn. As you progress you will learn to understand and incorporate the others better. If you think about air-to-air gunnery, the attacker needs to be able to "pull lead" on his victim in order to score a hit (assuming the bogey is manoeuvring). That in itself is complex. He has to correctly judge his closure rate, the speed and angle the bogey is at, and hope they continue to hold those variables. If they vary one of them the attackers solution will fail without adjustment (assuming spray and get lucky canon kills don't ruin your day). So you need to be unpredictable, and more than that to get best results you need to be able to manoeuvre when they cannot actually see you.
The situation you describe leads to a very high closure rate and a large speed differential. This means the attacker will have to pull extreme G loads to pull the requisite lead and get a solution. Often you will be well under his nose, and/or they will be riding the black-out tunnel, so they will have very limited ability to accurately track and anticipate where you're going to be. However, they can make an educated guess as to where you will be at firing time, aim there, fire, and if you haven't varied your trajectory, you may well get clobbered. So, the key is to be unpredictable, and make your move when they have a hard time adjusting their solution.
I suggest you do some reading on air-to-air gunnery at simhq, and understand the finer points of air-to-air gunnery, and that will give you valuable insights on how to foil those attacks.
http://www.simhq.com/_air/acc_library.htmlThe simplest and, IMO, the best way is to commence a flat low-G break turn (flat, or slightly diving) about 1.5 out, this makes it look like an easy shot to your attacker - and 99% of the time they will take the bait. when they get to about 1k-900 start progressively tightening up the break turn, stay flat and predictable. Notice now they will be almost in-plane with you (your wing angles relative to the ground are identical) and they are ready to fire. At about 600 out, you will more than likely will already be under the bogeys nose and he wont see what you're about to do - all in one smooth move, level out a little more (roll closer to level by 20-50 degrees) and pull hard Gs (you will be doing a climbing turn now) to get out of plane and well under the bandits nose and out of their bullet stream. They will now overshoot your wingline. Job done.
What happens next is the fun bit, but out of scope for this conversation