Do they scale or are zone set with like a range of enemy levels?
I can tell you how past Beth games worked. Since Fallout 4 uses the same engine as their older titles, I would imagine the game mechanics are similar.
Mostly, enemy encounters are based on leveled lists of actors. As the Player increases in level, so does the level of the enemies generated. Hard-coded encounters remain static regardless of player level. This would include named NPCs the players meets and the like. There are/were also encounter zones. These zones, usually defined in outdoor settings, would take on a level based on what level the players was when he/she first entered that zone. This would remain fixed throughout the game. Therefore spawned encounters within encounter zones would remain at the same level for the duration of the game regardless of the number of respawns.
This is how it is already for about (I'm guessing) 80% of encounters. Though for many, this will still not be enough as the player inevitably becomes over-powered. For example, I found in Skyrim, that at high levels, my player could slay a dragon with 2 arrows. I modified the game for myself (not a public mod) that boosted dragon health by a factor of 10. Then basic dragons went form 400 Health to 4000 and ancient dragons had over 12,000 health. Now that was a battle.
As an alternative, if the game is too easy, just ramp up the difficulty level. You don't even have to start a new game.
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So if I enter the Glowing Sea at level 1 the game generates enemies to match my lvl 1 char and keeps that enemies level even when I'm level 100+ and enter that area ?