There is no "standard" pitch. Your tarp, the terrain, and the weather will dictate the pitch du jour. Your tapered tarp will be pitched lower in the rear, which should be pointed into the weather. Campsites are rarely flat and one corner or another can end up in a hole or a slope. Sometimes you get lucky and can tie off to a log, etc. It is as much art as science.
I'm sure there are optimum length poles, but most use their trekking poles which can be adjusted to suit. Having the option for low pitches in bad weather and higher pitches in hot weather is a good thing.
Practice, practice, practice! My first tarp pitch looked like a drunk was at work. Learning your knots and good staking help a lot– especially when the wind picks up at 3AM. There's nothing like a nice taught pitch.