One of the great audiophile mysteries seems to revolve around how much to toe-in or out your loudspeakers.
I've seen everything from no toe-in to speakers aimed like headphones.
How does one determine the correct amount? The easy answer is by listening. But, that answer is waaaay too simplistic.
Listen for what?
First off, let's remind ourselves why we would toe-in the speakers at all. We point the speakers at our listening position to increase or decrease the perceived output of the tweeter. Because tweeters have very short wavelengths (like fractions of an inch), aiming them at us is akin to pointing a flashlight: the brightest light points directly at our eyes.
To make matters more interesting, it's important to note that all speakers are designed differently. Again, picture the tweeter like a flashlight. Some speakers have a narrow off-axis response—think of a very narrow beam of light—while others have a broad and smooth off-axis response (like our own FR20 and FR30s). The more narrow the beam the more toe-in is needed.
And....how far apart are your speakers? How live/dead is your room?
As you can see there are no easy rule-of-thumb answers that don't involve listening. Which is why in my Audiophile's guide books, The Stereo, and The Loudspeaker, I always instruct people to start with zero toe-in and, using proper reference materials, start pointing them towards the listening position in small increments until they sound natural.
In the end, you have to adjust them by ear, but having a bit of info and instruction helps a great deal.