Comparing Si & Se or Ni & Ne is the wrong way to go about it, IMO. Neither IxFP type is characterized by their tertiary.
I don't have the time or inclination at the moment to discuss the difference between Se & Ne, but I may come back at a later time, if I feel like it. Or just give me a call via a mention if you wanna this input. I had a long discussion with myself the other day in which I clarified all the functions & distinguished them from one another succinctly, but now I have forgotten the details; nonetheless, I am sure I can recall the gist.