I have one of these, and it seemed to be a nuisance of a major order. Put something of weight like coinage in it and walk, and it swings back and forth as you walk eventually banging into something you deem important, and painfully so. But this weekend I lucked upon the answer.
It isn't a simple bag pouch at all, if we consider a bag pouch as being something you tie upon your belt and let swing. This discovery is a bit difficult to describe in text, so please bear with me.
Instead of putting on your belt and then tying on the pouch, do this - open the tie strings, and thread your belt through each loop. Now, put whatever you wish in the pouch, grab the knots of the two strings, pull up and tie a simple overhand knot (maybe a more substantial knot like a square knot if your pouch is heavy). When you do the round pouch turns into a flat-mouthed pouch that nestles against your belt, and no more swinging and banging the naughty bits, and with the "opening ears" of the pattern, you need only loosen the knot a bit (easy when it's a simple overhand) to access your treasures. I should mention that I made mine from braintanned deerskin, so the ties/laces/cords have a lot of inherent friction, and a simple overhand as I tried to describe is all you need. I also have a 14thC "kidney" pouch with strap and buckle, and the Viking pouch is easier to use once I finally figured out how to wear it.
Hope this helps, I can't state that it's historically accurate, but experiential paleontology finds an occasional gem.