I prefer to have my head positioned as far back as possible / as far away from the sight as possible.
I have the zoom-toggle mapped to a button on my stick so that I can easily flick it on/off, and just adjust it to about 60-70%.
I never, ever use the zoom while fighting or shooting, or setting up my shots.
I occasionally use it to get a quick "snapshot" glimpse of a target, but even that's pretty rare. Mainly if I do use it it's to get a quick glimpse of a fleeing target that's essentially stationary in my sight.
To me, I find it much, MUCH more important to keep the "big picture" view I get by maximizing my FOV as much as possible. I have my FOV set at @105.
SA (as far as what's going on around me, rather than focusing too much on the guy in front of me) is more important than carefully lining up my sights on a target.
Zooming while shooting, or even while setting up my shot prior to shooting is very detrimental to the way I time my shots. Quite often if I shot while zoomed my target wouldn't even be in my view.