Another method that can work well with 2 harps is to put a fig.8 mic between them, with the plane of rejection facing the orchestra. You'll gain some of the attack that's lost when there's no spotter, and let your main pair or outriggers catch the 'bloom' or sustain of the harps, as intended by the composer/conductor. Fig.8 also helps with rejecting foot shuffles and pedal noises of the harpists, esp. if it's on a low stand 2.5 to 3 ft off the ground. Beware of the mic casting shadows on the sheet music that's inevitably located right where you'd like your mic stand to be !