Riding a Supermoto style motorcycle is different, and some people, mostly with road riding experience seem to have problems controlling the bike, therefore we explain. Supermoto is a unique form of racing and as such needs a unique riding style. Those who come from a motocross background normally do well on the dirt but not on the Tarmac, while road riders are good on the track but not on dirt. It's those who learn to blend the two styles who are more successful.
You can forget the knee-down technique. It makes you hang off too far and put too much unwanted pressure on the handlebars. As for leg-out, you have a choice. In some turns (the shower ones) having the foot out helps to balance the bike and move weight to the front to help the front tire be more planted, remember this is basically an off-road bike with huge suspension travel so the more we can control the extent of the travel the better.In other faster turns you can leave your foot on the footpeg as motocross boots are bloody heavy to hold out in front of you all the time!
You can play around with these different positions in various types of corners to see which technique works for you. The other main point is your butt. There should be movement forwards and backwards as you enter and exit turns. When you approach a turn, move forward; as you exit, move back into the seat's natural dip.
Again this helps to control the suspension travel. As for hanging you butts off the seat, forget it. Keep it right in the middle of the seat, all the time, with the exception of the off-road sections. That's another story.