The comb filtering through the screen can be measured using 1/24 octave resolution in the 10-20kHz range, which isn't audible but can at least indicate what's going on. We can only resolve 1/3 to 1/6 octave combing, and being in the top octave of frequencies is especially inaudible (unless it's moving around). The 1/24 octave measurements show that the closer the speaker is to the material, the combing bands widen and shift down in frequency, both of which make it more audible. The reality check is that when you smooth it to 1/3 or 1/6 resolution, even at 1" the comb filtering effect no longer shows up (i.e. inaudible).
At greater 6-8" distances, at a 1/24 octave resolution the combing bands narrow and shift up in frequency, which would be less audible. Again, in the more realistic check of audibility, at 1/3 or 1/6 octave resolution, there isn't comb filtering to improve upon.
Therefore, for an RTA, sure, space it further. For hearing capabilities, it makes no difference.