It is the hot waxing of my sheaths that sets the leather in a kydex like manner which forms to the knife so that it can be held upside down and it wont shake out but will pull out easily when needed. There is no need for a retaining strap and the shape of the handle does not really give any place to effect any more retention than what the sheath itself does.
This is a short video I did some time back for another forum on the hot waxing

https://www.youtube.com/watch?v=r2jzIUNzWV0&feature=youtu.be