As Adam has said, the KEY is getting the meter to CLICK into the mount. When I first got mine, I thought the same as you...WTF, over? Why is it SO loose??? The key is to push it ALL THE WAY ON, until it clicks into place.
As for being "touchy", what you need to do is to find an O-ring that is the proper diameter to be a little BIGGER than the shaft of the adjustment knob and a little SMALLER than the inside diameter of the knob itself. Put that O-ring under the knob and then smush the knob knob down on top of the O-ring nice and snug. You will now see a significant difference in the amount of effort involved in turning the knob. It will stay in place much better. I also did that with ALL the knobs on my GT, particularly with the threshold knob, which tended to get "bumped" on me a lot out in the field. Now it takes a real premeditated desire to change the position of the knobs in order to actually change the position of the knobs.