GVMI with Sentinel-2 data: using B8 or B8A?

Hello. When obtaining the Global Vegetation Moisture Index (GVMI) using Sentinel-2 data, part of the literature mentions using B8, while another part uses B8A.

Which one would you recommend using?

It kind of depends on what you want:

B8 is 10m res has peak 842nm has bandwidth 140 (wide)
B8A is 20m res has peak 865nm has bandwidth 32 (narrow)

suggest B8
which is N in the formula they give in https://github.com/MCroci/agr-spectral-indices
((N + 0.1) - (S2 + 0.02)) / ((N + 0.1) + (S2 + 0.02))


Thanks for the reply!