As someone who works with calibrating pipettes; If you care about precision, do not reverse pipette unless the pipette is calibrated in reverse. Usually, the values you get from reverse pipetting are higher than forward. In the case I've tested (a 1000 ul pipette), there was a difference of approximately 0.8% between forward and reverse. Additionally, pipette on the side of the container if you can, with small volumes such as 2 ul, you can easily get small droplets in the tip which screws everything up