I've been to one h.s. baseball game and one h.s. softball game this season. I'm sure once playoffs start I will be to many more.
The ones I've seen have had generous strike zones. In the words of a good friend of mine, a well-respected umpire, if you want to walk, buy a dog.
I can't speak to the high or low part of the zone, but it usually extends a few inches off the plate, although consistent for every batter.
I covered a softball regional semifinal doubleheader last year where, for some reason, the same guy had the plate for both games, although the rest of the crew changed. I was told he was the top umpire in the local association. I'm not one to complain, but his zone moved all over the place. Two pitches in the exact same place would be called different things in the same at-bat. It seemed like when a pitch came in, he would flip a coin to decide if it was a ball or strike.
As one who doesn't care who wins a game, I can say that the incredible wandering zone didn't favor or hurt either team, although pitchers and batters on each team had moments of frustration.
But hey, I tried umpiring many years ago. It's very, very hard to do well. I was so bad I even knew it and decided I would not damage the game any further.