Fullscreen refresh rate not matching

Hello,

I recently bought a new 165Hz monitor with G-Sync, and decided to set it at 100Hz (yeah, i know this sounds very weird but believe me i have very good reasons to do so. please don't ask about why i want to do that thx :) ).
The problem is that when i play FF XIV, even tho i specify to the game which refresh rate i wanna have (in the resolution menu) which would be 2560x1440 (100Hz) it justs stay at 165Hz (i mesured it with a fps counter with vsync on).
So basically, the game completely ignores the refresh rate from nvidia control pannel and stays at 165Hz as long as i'm in full screen. And if i set it in borderless windowed mode, the problem is solved, but then G Sync won't work and i want it.
Anyone knows a fix to this very weird problem ?

Thx