In Assetto Corsa with onboard app open there are crosshairs centered exactly where the virtual avatar's eyes would be in game, as well as another set of crosshairs where your current seating position is. I use those crosshairs to set my seating my position in AC and it is very important for how I like my FFB to feel. If the virtual driver is not placed well in the car then this doesn't work, but for many cars it does. Is there something like this in AMS2 or a way to set my seat position to virtual driver's eyes? The default seating positions in AMS2 for me are almost always too low and too far back. Most of the time I'm just taking a close enough guess based on the position of the virtual driver as seen from the external view.
Is your monitor height set correctly? Your eyes should be at the half way point on the monitor. Using my calculated FOV it is very rare that I have to change the seat position up or down. I do tend to move the seat back a few notches to give me a more in car feel. For reference I am on a 35inch ultrawide wide using a fov of 73.