What determines the "gripping" strength of this design? I can get it to hold some things, but the slightest little bump will cause it to slide down or even worse, the latch opens. My printer is calibrated, all the dimensions are square on. I printed in PETG which is a very dimensionally stable filament. It just doesn't "grip" hard enough and seems to come open pretty dang easy. It doesn't seem near as stiff as yours does in the video.