I think climbing position has not only to do with duration and steepness, but also how the bike is setup to fit in the first place. Some geometries favor certain approaches.

Regardless of which position one climbs in, I think it's important to be relaxed and to maintain a sufficiently fast pedaling speed which allows you to finish the climb without having to reduce power. It's better to kick the power up as you near the top rather than having it trail off. So pick a sustainable pace and settle into it, keeping a little in reserve for a finishing kick.

I actually do climb "on the rivet," i.e. on the nose of the saddle, when it's steep enough that keeping the front wheel planted is an issue. When it's in the 15% range, I'm yanking on the bars pretty good with each pedal stroke (probably because I'm undergeared for my strength and weight), so scootching forward helps me stay on top of the pedals, get more power down, and keep traction on the rear while avoiding lifting the front.