I'd say being effective at reading E states is largely due to experience and how often you fly. It is very difficult to explain over writing just how to make it easier to read E. The icons are the indecators. Often times another good way is to judge how fast they are going when you first enter the merge. How fast did they pull the loop after the merge, can they pull a second loop? Can you pull a second loop?
A lot of times you have to kill another players E by going into a verticle spiral climb. This gets the player to over compensate trying to make the lead shot, they will typically get ropped If you can keep it close enough to make them think they will get a shot. If there is a player with a lot of E, then when you pull a spiral climb you really have to loop harder and then pull up, then loop hard again and pull up, then go into the spiral climb, so they lose E trying to make the shot. This takes a lot of practice and really mostly.
If you notice the way I fly. I like to make my oppenents think they have a shot. Ill cut it extremly close because if they attempt to make the shot, I know it will kill their E faster than mine and I can pull loops easier over them. I'll give them an extremely tough shot to make ( 95% they will miss) and this sets me up with better E and a better position. I've developed that well and it's largely from experience, knowing exactly how people are gonna fly.
You can also use defense maneuvers when they are on your 6 and use their E to their disadvantage. So if you got someone closing behind you, pull that nose down turn, when they follow they will be blacking out then with timing, you do a nice roll right over them and jump their 6. At this point it's pretty easy to be able to tell how much E they have . this is my favorite move in the game because if they kill their E and go into a rolling scissors then you have a chance to win because you are initially going slower. You can really get a lot of great kills pulling this move.
Always in every fight. Especially if you see a low con trying to climb up to you. Always push the nose down first facing them, this will give you a slight boast of extra tiny speed which can give you the extra bit to pull off a loop. If I got a fast plane coming from below to attack with a lot of E, normally I'll turn down to the right or the left which ever direction they are coming from and I'll turn nose down inside first, to get some E real quick, then I'll proceed to pull up into a spiral climb or strong half loop depending on how I judge their E and speed.
These are all some ways you can kind of recognize E states and perform a move to lower their E for your advanatage. Like I said though, it's kind of hard to explain by writing. But next time I see ya we can go in the DA or something or you can ride in my plane.
I'll tell ya this too. The one who can maneuver with loops and instead of going for tough shots goes for the loop around will win the fight. You can destroy their E using loop fighting techniques but I'll have to show you in the game.