So if the spray pattern is better, can I assume, with better atomization, that the ECM will adjust for that somehow and not run hotter due to making more power. I had an issue on another X1 where the head temp sensor was telling the ECM to dump in more fuel to keep the engine cooler. As a result the O2 sensor was getting fouled badly and then it just went into a loop of one sensor trying to compensate for another until it just ran shittier and shittier.
However, I am getting excited at these results.
The better atomisation will make the mixture more homogeneous giving you a faster (or more consistent) burn and with that you can reduce ignition advance which means less work done before the piston reaches TDC which means more mpg at part throttle and more power (all things being equal) at WOT.
But back to your X1 issue, although there are corrections for engine temperature and air temperature, the closed loop control at part throttle will correct back to stoichiometric and any errors will be lumped together in the AFV, which is a great measurement to warn of any issues that need further investigation.