Terror Zone Tier List - Question

hi

About the Terror Zone Tier List: forums/diablo-2-resurrected-terror-zone ... 596357.htm

Is the tier assigned to the terror zone as a whole or to each sub-area individually?

For the ones I've looked at in detail, all sub-areas of the same zone have the same tier... and it seems strange to me that, in the same Terror Zone, the dungeons and the "open area", which usually have a lower density of monsters, have the same tier

For example,

Cold Plains,

Cave Level 1 and

Cave Level 2, which are part of the same Terror Zone, both have Tier B.
In my opinion, Cavern Level 1 and Cavern Level 2 have a considerably higher density of monsters than

Cold Plains.... (Shouldn't

Cold Plains be probably one tier lower ?)

I seem to recall that the game spawns uniques & champions in a radius relatively close to the player when you go to a zone so you can still get most of the benefit from open areas without going through the entire zone.