As a side note, the wingtip missiles look off as well, in terms of the wing twist at the tip. The missile in the left of the art looks angled down while that on the right looks angled up.
As a side note, have you ever looked at some of the sketches by Keith Ferris or other aviation artists, where they layout the aircraft as a drawing with many cross sections drawn in perspective and then paint over it? It's as if they "draft" the structure of the aircraft, add in the details, then paint it.
Below is a link to his main page and a link to the second page of his studio link and you can sort of see how he lays out his paintings.
http://www.keithferrisart.com/Default.asp
http://keithferrisart.com/thestudio2.htm
You may already know most of this, but I'm just trying to offer some help as you're putting a lot of work into it and I think you're making good progress. Sometimes when I sketch aircraft and I can't quite get the basics laid out correctly, I use 3D CAD to get the basic cross sections in place then rotate it, as opposed to drawing it, to get the proper perspective I want for reference. You can even do that with paper or cardboard. Draw some cross sections on cardboard and space them out properly on a pencil, straw, or whatever is available to you and cut out the wings and tails and tape them on and rotate it to get a feel for how they look in relation to each other. I'm just trying to offer some suggestions that might help you out, in much the same way artists and animators use those pose-able wooden figures to get human anatomy right. Keep going!!
Edit: Something else I hadn't really thought of until now is, if you are using cardboard, you can draw the top view and side view and cut them out and cut one halfway down from the tail and the other halfway down from the nose and slide them together. Throw on some cross sections and the tail placement and you would have a good quick model for reference, sort of like those simple balsa planes I used to buy when I was kid (With the exception of the cross sections

)
Oh, and as long as you're a glutton for punishment, when I'm sketching a design I'm making, I like to show sort of a perspective top view like you've done, then have the wingman peeling off so you can also see a perspective bottom view. It helps "flesh" out the design IMHO.