Personally i think it would be better if all the faces used the same angle rather then each looking at the camera individually
So get the angle from the foliage mesh as a whole to the camera then set all faces to use this angle around there individual center points
I did make a crude image to show my thinking
- The dot represents the camera and the hex shape is representing faces of a mesh be it a sphere ect in there original pos/angle
- Shows the faces in billboard facing the camera
- If you make the billboards bigger you can lead to intersections shown in red
- Instead if you have all the faces billboards using one angle to face the camera and not per face. Aka the angle from the mesh as a whole to the camera position
- So even with there bigger size there less likely to clip and if they do like shown there would be faces in front covering it for the most part
Regardless weather it looks better or not i assume finding the angle from the mesh to the camera is easier then a per face basis