To describe the situation further:
This is a single player game.
The hole down was a narrow gap with grass on both sides. I could see the cave system below in the minimap. It appeared to extend further below the maps and I WAS looking for bat scrolls and gems. I couldn't see what was down the hole until I dropped down. The previous areas had pre-positioned platforms along the length of the hole that I figured would be in this one.
The hole stretched down about 6 body lengths down before ending in a pool of water and a dead end cul de sac. The area appeared to be back dropped with rock. I placed a platform throughout the entire area and it kept falling to the ground. I tried to place one in the gap and it wouldn't form at all.. I build a stair case of two crates but, couldn't get any further crates to form. I tried to jump and place crates below me to no avail.
As for the thawing woods area, in the first chunk of the region, I had a sky- island in the middle, far out of reach of the ground and a cliff face about 2/3rds of the way into the map. there was some back drop but, my first platform fell. A Second farther into the backdrop did hold. About this time, I figured there might be a problem with platforms or their minimum required spawn space.
I'll hand it to you that the underground spaces are probably more realistic but, you'll start having lots of dead people littering the catacombs as they get stuck in the more intricate geometries.