OK SkyChimp, let me explain exactly where I don't thing your argument holds water.
Alt cap is 6k. I'm flying around at 5,000 feet, and when I merge with an enemy, I can't do an immelman.
Alt cap is 8k. I'm flying around at 7,000 feet, and when I merge with and enemy, I can't do an immelman.
It doesn't matter WHAT the alt cap is, if you fly right at/under it, you can't perform and immelman. It could be 20k, and if you fly at 19k you can't do an immelman.
Here's some advice if you just HAVE to do an immelman on the merge. When you see a co-alt enemy and both of you at/near the alt cap, dive down some (1-2k), chop throttle, reverse rudder (whatever, just BLEED E) and do your immelman. OR stay fast, dive down closer to 2-3k, and do your immelman. They have 2 choices, nose down to you, or fly off. If they nose down, they gonna be fast, and can't turn with you, as you are slower, and have the better turn radius. You now are in a much better position, and can maneuver for the kill. They can fly off, but won't get far w/ the 30 second rule, AND you are not that much slower than they are, and they won't be able to create much seperation. You will be behind them, and again, have the advantage.