Best way to get accurate rake angle on speakers

If you have good speakers then the dispersion should be such that the presentation is not overly sensitive to rake. I'd suggest to have the tweeters a little above ear level (about a foot) when seated - this means that it will usually still sound good when standing. I prefer speakers level and higher up rather than low but raked as I find a raked setup has a limited sweetspot.

Use your ears to determine speaker orientation that sounds best where you listen from.

I am using Vandersteen 5A's. In experimenting, after raising the rear of the speakers - maybe 1/8 of an inch or less, the sound went from excellent to jaw dropping unbelievable.