I think the HS-and-club coach connections run quite deep. And I don't mean "just" head coaches, but also assistants and JV/freshman coaches as well.
For example, just reading the bios of the Paramount coaches (
https://www.paramountvbc.com/coaches), I see current/former ties to Potomac School, Flint Hill, Chantilly, and Trinity Christian.
DMV Elite (
https://www.dmvelitevbc.org/page/show/8225070): Thomas Jefferson, Fairfax (former), Riverside, Stone Bridge, and Kellam (former)
VA Juniors (
https://www.vajuniors.com/page/show/1453660-va-junior-coaches): Westfield (former), Langley, Lightridge, Flint Hill (former)
Loudoun Elite: Centreville, Riverside
I know the Arrington name used to run deep at Flint Hill ... and Metro, but I believe she's now at Jackson-Reed (with her daughter ... maybe?). The varsity coach at Flint Hill that replaced her has been a boys coach at The St. James. I know other TSJ coaches are or have been at schools like Edison, Justice, James Madison HS, Washington Adventist U., George Washington U. (former).
I'm sure there are many others, but this is just a snapshot of what I've seen when looking at clubs for my kid.
Lots of these folks are former college players too. Every bit of experience they have can give them an edge in the high school game.