Also be very careful when it comes to servicing the filter. They need re-oiling and if over done it can mess up your MAF sensor if your car has one.
Pipercross do a dry type filter for vag group cars that avoids that problem. 
So the piper cross filter can stop more dirt particles than a OEM paper one?
What about the natural flow of oil vapour in the the induction?
If the engine breathes heavy due to wear and tear does that not just make the dry one wet also?
I love how VAG spent millions of pounds testing and trying different things and these MK2 are getting on abit so tollerences are getting near zero factor.
Lets explore the smoothing of the air box!
Those little squares are designed to collect dust and dirt.
Has anyone seen those all ways dirty and full of crap when changing a air filter?
What happens when they are smoothed out?
I'm guessing most of the dirt gets sucked in due those buffer square stoping what was designed to catch dirt the air box?
Most people are better of getting a direct air feed from outside the bay so no heat soak can go into the induction.
Instead of trying to move more CFM through a standard hole which is usually hotter and dirtier air, why not try and find a colder more oxygenated denser air flow source, like using a Ram scoop directly being feed from outside? Or shielding the heat soak away from the induction pipe to throttle body.
