In the case of an orifice, like we have in the fuel return system of the RV-12, if the fuel pressure stays constant, the actual flow through the orifice will be relatively constant.
Because of this, the K factor can be adjusted to calibrate the system and artificially compensate for the return flow. Do this by utilizing the standard calibration procedure in your EFIS documentation. This procedure is always required whether there is a return flow or not because simply using the K factor of the sensor does not account of the many other installation variables that exist.
When properly calibrated, the fuel computer in the RV-12 is quite accurate... in cruise flight (the only time it is really all that important..... for use on longer cross country flights). It does have some error when doing a lot of pattern work because idle and lower power settings do result in a different fuel pressure, but even then it is not off by very much, and will always have error in the conservative direction (will say you have less fuel remaining than you really do).
Any opinions expressed in this message are my own and not necessarily those of my employer.
RV-6A (aka "Junkyard Special ")