Having a way to flip orientation in the native parameters is a good suggestion. I’ll file that in our features database. Here’s one potential workaround in the meantime:
-In the native parameter controls, open the Composite group and change the Composite Style to Alpha + Apply Mode. This will cause the particles to render with a live alpha channel instead of compositing over the background as they are rendered. Then since you are in Avid you need to set the Background menu at the top of the effect to None. This is the general way to tell a BCC effect in Avid to preserve a live alpha channel to pass on to another stacked effect. Then Alt+Drag BCC Fast Flipper effect onto the particles (or BCC DVE Basic) to perform the flip. Using a BCC or Sapphire effect for the flipping is important since they know now to interpret the live alpha channel generated by the preceding effect. Note that depending on the apply mode/particle color settings you used, you may see some differences in the particle colors by using this delayed compositing approach, and in some cases you might want to tack on a 3rd effect in the stack such as BCC Composite to fine tune the compositing details.