Heh, I'm blushing at my respected nerdiness.
Anyway, here's a frontal shot from the film...
I took the image from Tech Commentaries, which if you need an anal-retentive detail answered they've generally got the best info (if they covered the material). They tend to try to "explain" things too in Earth terms without just having leeway for it being a film, having mistakes, etc., but they do inspect stuff closely so they're a good resource for that at least.
Here's what it says about the TIE Lasers:
Close-up views of the cockpit balls of a standard TIE fighter and a TIE X1. The laser cannons are the twin apertures immediately beneath the main viewport. The cannons on the X1 end in orange structures which were used on all the fighters based at the first Death Star. The laser cannons of TIEs in The Empire Strikes Back and Return of the Jedi are simpler and colourless.
Now, typical anal behavior, they're trying some kind of explanation with it like it was a difference in fighter design between the films. Obviously it's simpler than that and the vacuformed fighters in ESB and Jedi just missed some details because they realized the models from the first film had more detail, etc.
Anyway, it appears that no matter what, the new sculpt laser piece on the TIE Fighters has (it's modded from the vintage sculpt noticeably to remove the light-up feature) some detail flaws. I didn't even notice this till it was brought up by you guys. It's a little detail and looks weird if you stare at it, but I'd go past it pretty much.
I like the fighter though it's not without flaw... If I were to review it I could certainly pick it apart for what they COULD have fixed for us for $40.
Hell, evne for $30 little stuff coudl get fixed just because, but $40 it was and I'd still buy a 2nd at that price... Sad to say.