head position and sun position

SO..... how does the sun position effect my groups?  if the sun is the left will my groups move right or left?

Another problem i think i'm having is keeping my head from leaning. How do you insure your head in straight and level? Any self checks?

thanks

Iron Sights the sun will tend to wash out the side of the front sight that it is on.  This will cause you to center the "skinnier" front sight to the side of the sun and your shots will "follow the sun".  You may also experience elevation issues with a high sun.  Blackening your sights with soot from a carbide lamp helps reduce this effect.  Sight Black works too but I've been cautioned to wipe it off right after the match.

Head lean a little is ok if it is more natural for you but too much is bad.  Side to side too much and your inner ear starts to mess with your balance.
Leaning to the front to far and you get eye strain.

Iron sights in the open sun:
http://www.starreloaders.com/edhall/nwongmain/ironsightsurvey.html
You will find that to be a pretty comprehensive overview from some shooters who have fired a bunch of 10s at Canton and Camp Perry. You may find that "conventional wisdom" is not universally wise.

As to head position, I have found that (for me) this is very important to prevent group shift. I draw a circle on the lens of my shooting glasses, to keep my head in the same position.