There are as many ways to stand as there are angles to maintain your foot at when seated. If everyone with an opinion on what works for them answers, this could run many pages. So I am going to say nothing about what position you should have other than - if your back is rounded down, ie, hips rotated back as you reach forward, you are compressing your abdomen and restricting your ability to take full deep breaths. I was doing this without being aware of it on a commuter I had that was short on the top tube and had a long head tube. Made a huge4 gamble and had a stem made that was 2" longer than the longest at any bike shop. Stretched me out like a cat doing one of those stretches where it gets really long. And on hills - radical improvement - in breathing, in comfort and comfort late in hard rides.

So observe what you are doing and what you could do to get more torso elongation. Another trick - this from a swim coach who was also a physiology major grad student - exhale! She stressed that in freestyle, the exhale was far more important than the inhale. That 100% exhale and 25% inhale was radically better than 50% and 50%. What a gift! I forgot her name years ago but I hope I never lose sight of the importance of the exhale. (When I start dying on climbs, it's "Exhale!" A boost every time I remember.)