Ah, the wonderful ambiguity of the English language. As the documentation says:
which can of course mean a single aircraft close to and directly in front, or alternatively several aircraft both close to and directly in front. However, I stand corrected. :)
I'm not sure where I'd go to check, except through empirical observation.
When I'm running 100% AI traffic, and parked on the runway at Atlanta Hartsfield, no autogen (can't stand the 200 foot trees), in the MS Trike, I'm getting an average of 5.5 FPS. A combination, no doubt, of a complex airfield, downtown Atlanta buildings, and all that traffic.
If I head 10.1 miles south, to Walker Field, no aircraft or buildings in sight, then I average 14 FPS. So that's almost three times better, but then there are no buildings in sight, so my mediocre FPS must just be down to the AI aircraft that are out of sight but possibly not out of FSX's mind.
If I then set my AI slider to 0%, my FPS goes up to 50.
So although that's a bit of a 'quick and dirty' experiment, when I'm getting only 14 in the Georgia boonies with distant AI traffic, but 50 when I remove all traffic, it looks like distant AI is reducing my performance by a factor of 3 to 4. Moving into sight of all those planes, and jetways, and downtown, makes it worse by another factor of two to three.
So that supports my reasoning that it would be nice to be able selectively to put all that AI traffic, the stuff that's out of sight, also out of mind. But if you can't do it I understand, you obviously have your own specific priorities.
On the question of AI, I do sometimes wonder whether to switch to MyTrafficX - I have both that and Ultimate Traffic. It's just that I'm a bit of a geek when it comes to real-world traffic, and when I fly into the Isle of Man and see an Alitalia plane, it sort of it ruins my day. I know, get a life! :(
Paul M