Like your mother said, stand up straight. Open up your chest and throw back your shoulders. This will provide you with the proper platform for the apex of your control frame. If you do this, your glider will have a much better base upon which to rest. You won't have to hold up the glider with your hands, but (in no wind) it will rest securely on your shoulders.

If you slump down, the glider will not be as high above your head. Standing up straight gets the glider up higher. You want the glider up and ready to start pulling on your hang strap after you start running.

Once you have a steady base for your glider you can open your palms and place them on the leading edges of the down tubes (no need to grip with the grapevine grip). You can pull back with your palms open to bring the glider nose down to the proper attitude for launch.

You can bring the glider nose down until the base bar is a few inches from your ankles. You won't trip over the base bar when you start running, even though it is that close.

These statements apply when there is little to no wind on launch and you have to create most or all of the "wind" yourself. If launch conditions are windy, you will likely have to grip the downtubes to help steady the glider. But you can still use yaw, roll, and pitch movements (not just brute force) to control the glider resting on the base of your shoulders.

All these things can be done before your launch and when you have all the time you need to think about your launch and do the things that properly prepare you for the launch. These are not something that you have to do in a split second without consciously thinking about it. They give you the proper preparation, so that when you actually launch you are in the best position to do what you have to do next.