Are zones 'fixed' at a certain power level or do they scale at all?

I’ve tried to look into this and most every answer gives a soft or even a firm ‘no’, there is no level scaling. Zones have a suggested power level (SPL) and a fixed difficulty that’s supposed to make a reasonable challenge at that power level.

But I just encountered something that makes me question it.

I’m on my first play through and I really want to face a reasonable challenge throughout. Rather than adjusting the combat difficulty, I’ve just been gating my own power growth by no spending points. I’ve finished half the zones in England and chasing after every map marker (mystery, artifact and treasure) had started putting my level way over the top. So I stopped spending my skill points as I got them and even refunded some to go back down to a zone’s suggested level.

Then I came across some enemies that I couldn’t beat and beefed up my power level in response to let me advance without having to come back later. Details in the spoiler tag:

So long story short, I was at Power Level 230 before getting back to the southern England story line.

Alternate question title:

Is Suthsexe supposed to be ‘skull’ difficulty?

I committed to Suthsexe at the alliance map and travelled down there via the Lunden docks. After I was in zone for a bit, I remembered my Power Level 230 was 70 over the suggested 160. So I refunded a bunch of skill points.

Then I noticed every enemy had a red skull icon next to their health and stun bars and took about twice as many hits as enemies had previously.

So is Suthsexe supposed to be way harder than previous zones when done ‘on level’? Or did I trip some scaling mechanism into juicing up the enemies there before nerfing myself?