I think they work out how much fuel is needed for 2bar and then just allow the ecu to keep adding the same amount until the rev limiter once the map sensor is maxed out. End up running rich at the top end for safety.

One of many benefits of going aftermarket ecu is you can use 4 bar map sensors, I’m going to be using a Bosch 4 bar map sensor on my next ecu and it will fit in place of my air temp sensor as the Bosch map sensor can read pressure and temperature