the wall/fence on the right of PNC Park in Pittsburgh

There is not a significant wall there, as is generally the case in (purpose-built) MLB parks. Instead, you have seating; there is railing to demarcate where fans can be as opposed to the playing field, but not a wall. It is traditional in baseball parks to allow fans to sit at field level and see the game; injuries to fans from batted balls (or thrown bats) has led to some netting being in place at most parks, usually at least extending to the dugouts now, but nothing further to interfere from seeing the field.

From this image (see link to MLBCathedrals twitter for full res), you can see the railing from behind. The blueish colored railing is still railing - just wtih some padding on it; and from other pictures including that on Wikipedia you can clearly see people with their arms resting on it, so it's around 4 feet high there.

The dugout area (yellow arrow) will typically be around the same height (around a person's height), so that it's not disturbing the view of the seats in row 5 or 6 (whatever row it goes back to).