This question was spurred by watching someone creating a portal on a hill in the overworld, and spawning above a sea of lava. I thought the two co-ordinates were related somehow.
In short does the Y co-ordinate of your overland portal effect the nether portal Y co-ordinate?
Best Answer
No, the height is in practically no way correlated between the two dimensions. As the relevant Minecraft wiki article explains, Minecraft will try to find the valid area that's closest to the destination X and Z coordinates. To be valid, the area needs to have a flat solid ground and enough space to accomodate the destination portal.
Only in the rare care of no valid area being available in the general neighborhood of your destination will Minecraft use your current height as the generated portal height, and only if it's in the 70-118 range (= above sea level).
Be aware that this only happens if there's no already active portal in roughly a square overworld kilometer, otherwise Minecraft will simply use the existing portals.
If you find the automated placement unsatisfactory, you can always DIY.