Excellent Question!
When working with particles traces there are basically two different types. Traces that have mass and traces that don't.
When you are using massless traces (which is the type you are using now), this is actually defining where you want the trace to go through at the plane where you placed your seed points. So, as you noticed the trace will still start from the inlet and work towards the outlet, but it will go through the seed points that you positioned on your plane.
If you wanted to model the traces starting at the location of your seed points, try turning on massed particles traces. When defining your massed particles make sure that it has a density that is the same as the fluid and the radius is small. This should allow you to start the traces at your seed point and it will then progress towards the outlet.
Give that a try and let me know how it works out for you!
-Royce
