Meanwhile, I have a suggestion.
I play with this mod, including almost all the submods.
But, the reforming Nazgul; they should reform, but it takes a while in the books.
After being swept away at the Ford of Bruinen, it takes a few months for them to reform, and after Eowyn "slays" the Witch King, he is not reformed for the Last Battle, there is specifically only eight Nazgul there and racing to prevent Frodo as their master becomes aware of him.
Perhaps 2-turn delay in respawning?