My twin spark gap is totally adjustable when running the Coil from left to right and around in circles and I can record it if you to show you, that when it is sometimes closer to the one side(Shorter spark gap)And away from the other side even to max power the way it fires is different from if it were say,The same distance from each leg to middle conductor at max(distance) power will most definately not fire at the same frequency.My guess is that if the first gap fires fast because the air is ironised quicker and the spark jumps though less conductive air but smaller gap,Then fast again into the center "Good" conductor then fires over a long distance again though less conductive air and alters the fire rate again and the frequency, then fast into the other leg of the gap thus I belive by firing twice, the the frequency changes twice.My Tesla Coil does not go above 10cm with one gap on my setup.