The general advice provided to me, and relayed by me is eyes centered @ 2/3th of the screen.
The best advice received and relayed by me regarding posture might surprise you.
If you struggle with posture, stop caring about what other people might think about your posture. Changing/Tweaking posture all the time might look bad, but it also tends to mitigate the effects of being frozen in bad posture(!) The health impact is too significant to ignore.
Yeah I think the only ergonomic advice I believe anymore is that there does not exist a position that is ergonomic to sustain for more than a couple hours. Humans are not evolved to stay stationary, few mammals are really.
