Make sure you have your Mirages down
1. Set the bag straight about belly heigth
2. Keep your setting leg in the air and
make a little hop with your support leg towards the bag. e.g. you set with the right leg then you hop with the left leg to the right. (hope this is clear

) The hop is crucial and creates the room for the dex
3. Jump hard of your support leg so it passes over the bag
4. Land and catch the bag on your setting leg
Learn this trick on both sides

and also from clipper and same side.
Symp. Mirage is a great trick to draw breath in a run.