The trackview labels for PRT Volume read “??”
Hah! Really.
Obviously, the first is the Render Spacing, the second and third are Shell Start and Thickness.
The PRT Volume is a C++ plugin, obviously we forgot to include some info in the paramBlock.
Thanks for noticing!
No problem, I had a double take, I was out on a limb playing with animated spacing when I saw it, I didn’t check any of the other PRT objects.
This also led me to wonder, is it at all possible to attach the propagation point to the PRTs pivot? So for instance if I centered the pivot in the middle of the filled volume the particle would grow out from there instead of what seems to be the center bottom (or the local 0,0,0) of the PRT Volume object? Or if say I rotated the pivot that the direction would change with it. It sure would make it easier to align the grid pattern to say a camera 
. You would have 100% control over the direction, would be very handy.
I also noticed that moving the PRT Volume pivot also moves the icon, I have no idea if this was by design or not.
The only thing you could do (AFAIK) is add an XForm modifier to the source mesh and rotate its gizmo. Since the PRT Volume uses the Object Space of the source object, modifying the geometry relatively to the local 0,0,0 of the object will also modify the particle grid’s orientation. The pivots of the source or the PRT Volume should not affect the distribution of particles.
I don’t think this approach would be very convenient for practical effects though…