TBI = Throttle Body Injection

Not many cars were TBI after the late eighties. The first wave of replacement for carburetors was single injector in the throttle body, followed by multi point injection in the intake runners. The reason I brought up carbs and TBI is that turbulence induced upstream of the throttle plate will be pretty much dissipated by the time it gets to the injector in a long and curved intake runner (multipoint). I also doubt there will be much turbulence remaining just downstream of the throttle plate at small angles. So the window for such a device to positively affect mixing is not wide.

If you measured your fuel economy over 8 months, I suspect there are seasonal effects in your data. Things like humidity and temperature will affect the efficiency of the engine. Also, some parasitics like air conditioning are not consistent from season to season. The condition of your air filter, engine oil, and filter will also introduce variation in your data.