I have JED set up to start me in the nether (dim-1) and if I die in the nether, to respawn me in the nether, not the overworld, but when I die in the nether, I'm returned to the overworld.

Here's my JED config and here's the dimensions.json file. Those are the only two files I have in the JED folder in the config file.
Hopefully this is a simple matter of me misunderstanding something or missing a change that's come about in the newer versions. That json I'm using is from a while ago..

JED version 1.6.0-dev.20180527.185104
Forge version 14.23.4.2705
Biomes O' Plenty version 7.0.1.2391

Your config was using the JED 1.5.x format, and also there was one unpaired double quote in DIM 1.
Here is a fixed version (untested though): https://pastebin.com/uvTzhAkK

Edit: The changes to the config and commands in 1.6.0 are listed here: https://pastebin.com/raw/28jeWZyv

You're a godsend. Works perfectly now.