Portals do not use Logical Height field from Dimension to place portals.

[klinbee]

I see that a y-range is being worked on, which will help, but default behavior for portal placement in dimensions is based on the dimension's logical height.

Without this, the portal will just default place the portal on the top of the height map. If a nether-like dimension is made, this results on all portals being on the roof, unless the world height (available range to place blocks) is lowered to the roof. But that means that it forces dimensions to either have the chance of a portal going to the roof (by not lowering the height), or allows the player to soft-lock themself by getting up on the roof through methods like pearl clipping (by lowering the height).