RE: Learning to use a hi-start
You really don't need anything but your feet to work out how far back to pull the hi-start.
Just walk back farther each launch until you get adequate line tension to do the job. Then add a couple of paces to however many that launch took. That number of paces will work all day. Now.........
Different wind speeds give different launch heights. On windy days you can actually add extension. And some really windy days you want to shorten your walk. You're going to get extra extension whether you want it or not. OK, most newbies don't fly those days, but someday..............