The maf "counts" every piece of air coming in. The base map for a 7m assumes the stander pumping losses. But if you rewrite the map and use the stock maf as the measuring device, it can tweak the load cell values. The algorithm in the basemaps already uses the stock karmann maf log with it's factory cross sectional area. So the formula already exists with the stock maf measuring device as a "constant". Pressure and temp will be a known variable in a certain range. Rpm is also a known Input value. So using all the known values, the ve of the engine will dictate how much air is ingested or pulled past the maf. So let's say, 1000rpm, 72*f, 100% tps, 0psig shows 190hz on the fuel map load cell. If you ported the head, went ffi, long tube exh mani, or otherwise changed airflow values, the only indicator will be the maf signal. All the inputs being the same as before, perhaps the karmann output shows up as 210hz. If you're rewriting the base map with the stock maf in place, it will slowly change that load cell every time you're in it. If you weight the values lightly, it may change to 192hz next time. Then the next time you're driving, it'll rewrite to 195hz. And so on until the karmann maf input value matches the value on the load cell on the base map. So this can be how you compensate for new cams or head work.
The map sensor would already assume your ve is a known constant. Which it's Not if you change any part of the engine which affects pumping losses. A turbo is not though. As it was explained to me, 2 atmospheres can only force its way into an engine so fast, regardless of what is producing that pressure (61mm, 76mm, m190, another planet). So at 2atm, your ve can only double. It can't flow ingest more than 2x it's ve that it had at 1atm.
But thats just my interpretation. I might be way off. Lol