In FKKVS you can adjust nonlinear injectors to give a linear fuel output.
The X-axis of FKKVS shows the injection time in ms (=> load), Y-axis shows RPM.
If the mounted injector is linear, the values in FKKVS are all set to 1.
If the injector is nonlinear and gives you a lean or a rich AFR mixture in a area, you must adjust the values in the affected map region, to linearize it.
Increase the values in a case of lean AFR to make it richer.
Decrement it, if it is to rich and you want to make it leaner.
Here an example for the original RS4 injectors, which gives a lean AFR in the low load area.
To compensate this behaviour, the values until 1.5 ms are increased.