Hi. Would anyone have any tips to prevent my camera from rotating/slipping down when in portrait orientation? I use an L bracket however I've noticed particularly when using the 70-200 it will very slowly begin to pivot downwards making shots of 10 seconds plus almost impossible to make. I have tried different screws to hold the plate in place and have got them as hand tight as I can. I'm wary about over tightening in case I strip the threads or something.