Nick - re: sitting back more.
You will need a wider stance.
if your feet are wider, and knees out, it puts the hips in a position to drop down and back.
You also need to have the bar lower on your back.
Only problem with this is that you will also be leaning forward more at the hips (ie your chest close to your knees.)
Rippetoe teaches this method of sitting back and hip drive etc etc.
Up to you which way you go, but as I'm sure Markos will tell you, changing your technique to chase a few KG usually ends up with injuries or losing kgs on another lift.
Give it a try with no or low weights if you want.
first few weeks of wider stance, knees out, arse back, hip drive gives mega pains in the hips, lower back, inner thighs and depending on your bar and hand position, you might get elbow and shoulder pain.