That separation worries me a bit as well. My thinking is that I want the aperture to be as coherent as possible which means close together. One way that they handle this separation is to cross between lines lower than you would think which minimizes any issue. Also the crossover can be a fairly high slope so the transition region is minimized.

Finally, the general rule of thumb is to crossover no more than one wavelength center to center horizontal spacing between the two lines.

Jim