First, dilution factor is not a volume and does not have units.
Second, there are obviously two different definitions of "dilution factor" out there. Thus if you had, say, 1 mL of solution and diluted it to 10 mL, the dilution factor could be 10 (first definition) or 0.1 (second definition). Personally I would call that a 10-fold dilution.
The important thing is to be consistent with whichever definition you are using. And remember that dilution always reduces the concentration. So if your DF > 1, then C2 = C1/DF. If DF < 1, C2 = C1*DF.
Third, 9.99e-4 is not 0.0009 (but you corrected that).