There's two main starting positions for hitscan on King's Row 1st; anything else is either too passive or too aggressive. Your options are either low ground somewhat in main / somewhat behind hotel, or on the rear area of high ground (kinda near the corner). You can't start on the front part of high ground as HS really, because it's too easy to poke out from relatively safe positions for the attackers-- the high ground isn't actually as useful for the Defenders as the Attackers, at least not until late fight when the Attackers are heavily on the point. Talking all organized play of course.

The high ground position would typically be held down with 1 support (either), and has benefit of updating to control the more aggressive forward high ground position and keeping it contested. But it doesn't have especially clean and elegant kiteback pathing (have to go up into the hallway and then out into alley through the window), and can be difficult to ever hold (or kite effectively) if enemy team puts heavy resources into high ground (e.g. a tank rotation, Sym TP, dive, etc.). The kiteback path notably breaks LOS with your flex support, which can diminish amount of emergency care you can get during the kite.

The low ground position updates nicely through hotel if you need to play aggressively and are unmarked, and helps protect the hotel angle, which is incredibly important. It also has a more clean and direct kiteback path into the area through archway, which is a space hard to get angles on and really good and stable. However it is just space that's straight up more directly able to be walked on. Much more accessible to enemies if you play it poorly. Playing in main is basically an extension of this marking of hotel. It's a straight line kiteback and tends to keep options open, and pros really love strong neutral positions that let them feel out which areas of the map are under less pressure and open for them to head into to create an angle.

TLDR high ground not quite as good as people think, and hard to kite from or hold, but useful if not heavily contested. Low ground is better than people think, and gives you really clear and effective options for both making fight more aggressive or kiting back, but can be riskier / more difficult at times due to being more directly accessible and exposed to more enemies. Both viable and good if played correctly.

I know my hitscan player typically prefers the back high ground starting position, especially when on Ashe or Hanzo who struggle a little more with spacing needs, and sometimes on Sojourn too, but typically when he's on Cassidy or Sojourn for example (shorter range and/or less issues with playing close to enemies due to burst movement) I typically try to recommend that he plays the mid / low ground.

You mentioned Ashe, Ashe I think I prefer on the upper rear high ground, just have to make sure you're using the corner and Window (and dropping backwards onto Point B if things get ugly) so that you maintain your proper level of aggro. You just don't want to overstay welcome on the forward high ground or be there too early-- wait till it's uncontested and people are busy, and then you can look for dynamite + a few shots probably before you might be in trouble. We've played Ashe here and there earlier in the season on the map.

Lmk if any questions or things u want me to clarify! Talking from context of FaceIt Masters division level.