Re: What length Bipod do you prefer?
i like the 9-13 for getting high enough to clear some ground clutter, but carry a 13-27 in my pack getting above for grass for kneeling and sitting shots. only takes a few seconds to switch it out.
the 6-9 to me is just too short for using in the field - but in the end - it does depend on your terrain, how you address the rifle, your body build etc.
i guess you can always carry a couple of blocks of wood with you, if the 6-9 is too short, you can "shim it" by resting the legs on the blocks.
i do like the 6-9 from the bench. if your budget will only allow you buy one, try tying or duct taping a few sticks together at 6", 9" and 13" and go for a walk practicing your most probable scenarios, and which length is used the most. then you know which length bipod you'll need for most of your situations.