I have a scene where the camera flys over a forest at a low level (the trees are 2 plane trees). The view consists of trees going offscreen on the Left, Right and Bottom sides of the frame (the Top of the frame is basically empty sky above the forest). As the camera moves above the forest, certain trees which are going off the bottom of the frame 'pop' off the frame rather than staying visible as they move out of view.
I have tried adjusting the 'Expand' percentage from the default of 15%. I am now at 40% trying to get trees that don't pop off as they go out of view. I am not having a problem with trees popping on either the Left or Right sides of the frame.
In this case, it would be nice to have more control over the 'Expand' setting such that the user could specify expansion for the Left, Right, Top, and Bottom separately so as to minimize the number of trees calculated during rendering, while still allowing the user to remedy 'popping' trees. We'll see if a 40% expansion does the trick this time.