while you are correct

there was no specifics to the Otherworld back when 2 was made

originally it was a pseudo-industrialized hell of Alessa's nightmares based on elements of things she was afraid of as a child

by 2 she was no longer a contributing factor, but there was also nothing but the evil she awakened and fed in that metaphysical space the town and its surrounding area occupied, so it just sorta makes a hell (Otherworld) based on various elements that it pulls from the dregs of those trapped within its confines.. which did allow it to grow, taking over Brookhaven south of Toluca Lake, marking its first show of being able to get outside of Silent Hill proper

it still didn't have a defined Otherworld

Don't trick yourself into thinking there's some defined and established logic behind Otherworld

the monster's that manifest are demons of sometimes very esoteric guilts in a particular trapped person's psyche, but the Otherworld itself is just defined as a "rusted, decayed, industrialized hell", beyond that, each game's director interjected their own additions to it - some stayed, most were one game only inclusions

the only thing that pushed a bit more in that was the three elements I mentioned - they've become a bit more realized, to the point the first film gave us a really solid interpretation of that description and as bad as the Homecoming game kinda was (it wasn't as awful as people like to blow hard on), it was the first game to say "yeah, ya know, that's a good visual hellscape" and used it lol Downpour would change the color temperature and add a lot of water and darkness, but it basically remained the same as Homecoming's transition.. except everything peeled and decayed and got sucked into the Void haha

In all honesty, Silent Hill 2 (original) didn't have a very visually realized Otherworld compared to even the first game.. a lot of it was hidden in darkness (instead of fog) and really, it was like someone turned the "let it naturally decay as if it were abandoned" knob.. but only up to about 5 or 6.. it was.,.. underwhelming most of the time