I don't think much about my foot position when standing. I couldn't tell you whether they're flat or pointed down (or even pointed up). I do know that pulling up with your trailing foot is a part of the equation that seldom gets mentioned. Even with a conscious effort to pull up with that foot, though, I've never seen anyone pedal anything close to circles while standing, whether they believe they are or not. Standing is all about application of power, down and up, in my experience. Smooth circular pedaling requires something besides your feet to support the majority of your body weight, like your hinder planted on a saddle.
One other thing to keep in mind - when the going gets really tough, or you want to actually accelerate while standing and climbing, you'll find yourself pulling up on the handlebars, too. It helps force your downward moving foot to power through its stroke.