I set the Carrara render size to be the same as the iPhone screen (480x320 at that time). Then I positioned and sized the objects to render to fit in the scene. That way when the sprites were imported into the sprite sheet they were all the same size and resolution relative to each other. Originally, I tried filling the screen with each object to render. When my son brought it into the sprite sheet all the objects had to be resized. I also made sure that I didn’t rotate or move the camera once I started rendering. That way the perspective matched from sprite to sprite. I can share some screen grabs from the finished game if it helps. The game isn’t for sale any longer so I can’t share it with you.