Fleet wings are rectangular even though they travel in circular orbitals. They're anchored to the orbital circle at the front of the rectangle, and very large fleet wings (>100,000 ships) are so large that ships at the rear of the wing can be so far above the orbital that the front ships are moving in that they appear to be out of range of their target and don't appear to fire cannons or missiles. I don't know if this actually has an effect on combat or if it just affects the way combat is displayed.
george moromisato 12 Jul 2018:
This is improved in Era 4.4 by adding extra range to missiles. A better (future) solution is to have flexible formations that curve.