I learned the erect shooting position from the bench when I started shooting 375/416.  At the range in Fairbanks the seats were just like you described and you were almost laying behind the gun.  I use to take my own seat so I could sit erect behind the gun.  I remember shooting very many rounds through the 375 at one session almost always gave me a headache.  I finally found that a small sand bag between the rifle butt and the shoulder made long sessions at the bench a lot more comfortable.

Frank