MX Cornering Technique

I've been studying this but very little is said about upper body position in terms of side to side. "Lean into the turn" is occasionally mentioned but in every video I studied pro riders appear to be leaning away from the turn ... just a bit.

So if you were above the rider looking down, the riders sternum is somewhere b/t the gas cap and outside foot peg.

Any thoughts?

My opinion:
 
The best riders have taken enough diggers (crashes) to learn to go by what feels right and what has proven to work for them, and that will vary depending on the terrain.
 
The more of a berm (or anything that gives great traction and instills confidence) you have to press the tires up against, the more you can get away with extreme lean angles, and the rule of thumb with motorcycles is that the faster you go around a corner, the more you have to lean the bike.
 
The less fantastic traction is in the corners, the less you can reliably lean the bike and body over a great deal, so if traction feels iffy, the rider starts to cut back on the extreme leaning and positions his body to suit the less-than-perfect conditions.
There are many corners that are going to offer less-than-perfect conditions when riding off-road.
 
Leaning the bike more than the body is done when conditions call for it, be it the less-than-perfect traction due to ground conditions, or even the shape of the topography, itself.
You wouldn't want to lean both bike and body over to great angles like a MotoGP racer when you're on baked-hard ground with a layer of loose dust on top of it with no berm in sight.

Best $19 I ever spent, each time I read a chapter I get better and or more confident.  I live relatively close to the author's school, I should really go there sometime:
http://www.amazon.com/How-Ride-Off-Road-Motorcycles-Dual-Sport/dp/0760342733/ref=sr_1_1?ie=UTF8&qid=1382534843&sr=8-1&keywords=0760342733

General technique is body upright, inside leg out and forward for counterweighting, shoulders parallel with handlebar (though as YZEtc points out each turn will be different due to terrain, conditions, equipment, etc).  There's chapters on hill climbs too  .

I don't ride motocross, but do go fast sometimes.  I lean to the outside (Or lean the bike to the inside further than my body) when I'm uncertain about how much traction I have.  If the bike loses traction, I feel like I have more leverage to shift my weight to react than if I was leaned in more.  Worst case would be if I was leaned in too far and the bike slides, I would be under the bike.  

On the other hand, if the bike is leaned over too far, there is less traction available from the side knobs than if it was more upright and riding on the bigger knobs.  It is a balancing act.