[HELP NEEDED] Withering Presence / Spreading Rot / Blight

Hello. I would really appreciate if some1 could help me out with my concern.

So, I am playing low life witch occultist with chaos skills (BANE + ED).

I have withering presence ascendancy, and I also use spreading rot.

I am wondering how does wither work with this setup.

Do I understand correctly, that ascendancy gives me 1 wither stack every second being near a mob that will go up to 15 stacks after 15 seconds, or will every single wither stack be gone after 2 seconds duration)?

Does it cooperate with spreading rot + blight or is every duration calculated differently?

Like if I am near a monster and I use blight with ascendancy, do I inflict 2 wither stacks every second that go up to 15, or every stack lasts for 2 seconds and it disapear so I can never really get into 15 stacks?

If so, is it smarter to get rid of blight and just get wither with multi totems?

Thanks in advance for any help. Cheers