Your theory has some basis. A pitot tube and a pressure gauge is used to measure an airplanes airspeed. The incoming ram air pressurizes the Pitot tube and the pressure gage is calibrated to the correct conversion. That conversion for air velocity is P = (V/4005) ^2 for the density of air, a pressure measurement in inches of water, and velocity in Feet per Minute (FPM). Assuming that your plane was flying around 60 MPH then that is 5280 FPM. So crunching the numbers I get 1.74" of water or about 2" of fuel. This is not that significant and though noticeable I don't think it would be enough to richen it up to a dangerous point. From reading your startup procedure did you only fill the tank partially? If so that would add another inch or two of fuel head and 4" of fuel head is becoming significant.

Now that you know that your plane can tip stall, then you know you should add rudder on turns. This keeps the angle of attack the same on both tips so that it will stall straight. If uncomfortable using rudder then you can program them to turn with aileron, then add just a touch manually in steep turns.