okay, i really don't want to go into how MAF sensors works (at least not in this post) but focus on why polishing the MAF is so important. Both the Thermistor (thermal resistor) and the Hot-wire (tungsten wire) are very delicate components that measure the amount of air being pulled or pushed in the motor, they are so delicate that if there is ANY turbulence in the MAF as the air flows through it will send an incorrect signal to the ECM and the ECM will send the wrong signal to the injector drivers and so on. There are quire a few shops that polish or you can do it yourself if you have the tools and knowledge, but it's one of those mods that is worth its weight in gold iof you're a tuner like me, doesn't matter what the air does after the MAF because turbulence in the intake is a good thing, it holds the fuel in suspension with the air so it doesn't fall off and stick to the runners and lean out your mixture, enough of that. Aside from polishing the bore you want to radius the entrance to the MAF so there is no ledge anymore, just a nice smooth ramp for the air to hit, i usually don't give this one away but spray silicone inside the tubes where they connect to the MAF, this gives a nice smooth tube for airflow before it even gets to the MAF, have fun..
AND NEVER USE CARB CLEANER TO CLEAN THE MAF, use CRC MAF sensor cleaner.