It does make a suprising difference.
When the inlet valves open on the engine they create a depression (Or vacuum) the air from the atmosphere rushes in to fill the cylinders, however due to the length of the inlet manifold some air will still be rushing in. This pressure wave will be reflected by the inlet valve back along the inlet to the cone, which will reflect it back to the inlet valve. If the inlet valve is open at the time the reflected wave arrives it will assist in filling the cylinder. The pressure waves travel at the speed of sound.
The variable intake is there because the faster the engine is running the less time there will for the wave to be reflected back, hence it moves to the shorter position.
Its obviously slightly more complicated that than as the TS has 4 cylinders, and each cylinder has its own set of pressure waves.
Its far too complicated to explain much further but I hope you get the gist of it..
If anyone wants to c0ck up their tuned intake by fitting an aftermarket filter good luck to them..