Where does the $2$ in Ricci flow come from?

Question

I started learning about Ricci flow recently, which is always given as $$ \frac{\partial g}{\partial t}=-2\textrm{Ric}. $$ It would seem more natural to me to define Ricci flow instead by the equation $$ \frac{\partial g}{\partial t}=-\textrm{Ric}, $$ which omits the $2$. The only real difference in behavior between this flow and Ricci flow is that this one flows at half the rate. Wikipedia claims that the choice of $2$ in the equation is an arbitrary convention, but this is hard for me to stomach, since conventions in math are almost always motivated by something. Is there a good reason that Ricci flow is defined the way it is, or is the convention really arbitrary?