I wouldn't carry any large knife around the torso area as accidents can be quite severe if you fall over etc and the knife become loose or the sheath splits. Just keep your large knife in your backpack as chances are you will most likely want to remove your backpack (for improved comfort and stability) to carry out any knife work. If you need a large knife (machete parang etc) for moving through a jungle environment then this video might be worthwhile watching.

http://www.youtube.com/watch?v=eMLI6BhFV2c