Like I said, I've seen a couple posts before about the 3 different 1x sensitivities.
High sens = Iron Sights with no rear irons. This applies to guns without a rear iron sight installed, or have no rear iron sight slot.
Medium sens = Iron Sights with installed rear irons. This applies to guns that have a rear iron sight installed.
Low sens = 1x Optics.
EDIT: Here's a post that documents it https://www.reddit.com/r/EscapefromTarkov/comments/fxowag/mouse_sensitivity_what_actually_affects_it_and/
Considering the large difference between high and medium, I'd say its well worth testing.