I'm sure if you search zip tie mod in the a5 forum, you'll find all the info you need, if that is what your talking about.
Below is my interpretation of whats going on.
It essentially slows down the building of boost, and it seems the computer has more time to reduce the boost spike and add fueling. Once your past that spike the vnt vanes aren't trying to build boost so rapidly and can easier and more smoothly make minor adjustments to the amount of boost requested vs actual. On full throttle and most in between the turbo is not trying to make maximum boost, its trying to hold at a certain pressure. If it were to continue trying at maximum vane angles, it would seriously overboost. The zip tie seems to stop it from initially building so much boost, thus getting you past that lag... now why the computer initially wants so much boost without the fuel, I'm not sure.
I've had that lag for a long long time, but it doesnt bother me much at all. I've stared at the boost gauge and played with it for more time than I ever should have. That is the conclusion I have come up with.
Best way I can figure of getting rid of it, is a bigger turbo ! Haha