I can try to answer, but this is based on the non-Basic INFI Steel Heart II, and I'm not sure if there are many differences between the Basic and non-Basic sheaths.
The sheaths are a rather stout kydex design with a tie-down strap, with the option of a higher-rise carry, or a drop carry, by simply adding or removing the top portion of the drop portion of the belt loop. If worn in drop fashion, it can be unbuckled and unstrapped from the thigh around camp or any other time it doesn't need to be actually worn.
I personally think it's a nice, sturdy design, very secure, simple, and effective. I'm not sure about strapping it to a shoulder strap on a pack, as I'm only 5'6", so I don't have alot of shoulder strap room for knife carry for something the size of the Steel Heart, let alone a Battle Mistress. I haven't seen the Basic series sheath yet, but if it's similar in design and construction to the non-Basic line, they should be winners as well. Here's a rough image of the Steel Heart combo, the quality isn't the best, but it may help.
------------------
Don LeHue
The pen is mightier than the sword...outside of arm's reach. Modify radius accordingly for rifle.