Hi William,
I carry a bigger multi purpose throw bag with 8.5 ml rope and use 5ml or 6ml prussiks.
I generally stick to 3 wrap prussiks.
You have a valid concern. I don't really try to AMP up the friction to make up for smaller diameter baseline.
Jim
Most throw ropes are 6 to 7 mm and you shouldn't use anything smaller than 5 mm prussik cordage in a life saving situation. Prussik cordage similar in diameter to the throw rope doesn't hold so well, do you go with a different friction knot? Could you explain how that works? I know a couple of other friction knots so i'm more concerned with the similar diameter ropes question. Thank You!