25 feet away, I use my adjuster to set them and then fine tune them to my liking. You don't want them to cross or be to far apart also. I used to do testing here in So Cal to re register totaled vehicles and had a few aimers (mechanical ones and optical ones) and you can find an old Hoppy kit for fairly cheap and they work great.
I know it's a chevy site but, check it out.
Headlight Alignment - The 1947 - Present Chevrolet & GMC Truck Message Board Network
BTW, look at his tool wall........that's dedication