Most folks in the DA in this type of merge are totally blackedout when pulling back into the enemy plane, but not to the point that it is a sustained blackout. Learn to ride the G's your are pulling, keep in mind most DA'ers have lost sight of you due to this, and adjust your tactics from there. Force a remerge if possible.
I, on the other hand, prefer a very tight YoYo(though still riding the blackout G's) to converse some E to attain a remerge or rope.
There is no one way to merge, I've been very successful in just going into a climb rather than going immediately into a stall fight. Then again, I believe E-fighting to be the most effective dogfighting method.
Practice, practice, practice.
Film, Film, Film.
If he gets his "nose under" you on merge, look for an opprotunity to remerge or conserve your E by taking the vertical. Having altitude below you to play with increases your chance to use more defensive BMC/ACM and a possible rope.
Immelman's aren't the way to go, again in my opinion. Rather than doing one, try the YoYo approach. Just by taking an angle rather than straight loop you conserve energy.
It's my guess this is what is happening to you. You are burning off all your E performing an immelman, your opponent is above you or has more E, and is therefore in control of the fight or is simply getting a better angle on you because of this.
Also, always insist on the lightest loadout. There are many people who will say let's take 50% fuel and full gun package when in reality they are taking 25% with a lower gun package as lethality in the DA is set higher than the MA(this may be wrong at this point in time, but was true in the past). It's also a good idea to have a friend in the tower. Many people shoot off most of their rounds before engaging. These tactics are lame, but I have personally seen it done. Many DA'ers don't care about a fair fight, only shooting you down regardless if it's done on even terms or not(who needs bb's when you have hispanos).
Also consider a flat horizontal turn on the merge. Many people don't expect this, and due to their blackout you can come in from under with a decent speed.
And yes, on the merge you want to have as high of an E state as possible. This gives your more energy to burn in your initial pass and some to retain for manuveuring.
I consider myself a fair dueler at best, but I've had more than my fair share of wins. If you like I'd be willing to review any film you have and give some constructive critisism or practice with you in the DA. The latter will also help me remove the rust that I am currently covered in.
-swift
Just my 2 cents.