On new(er) aircraft, the tilt angle may be more precise, so the formula might work, but generally find that with the older radar equipment, tilt down 'til ground returns are received, then up a bit.
On the TriStar, about two degrees down on the dial at (for example) FL330 was about right.
Of course, you can scan the height of the cells as well, but this takes a bit more experience with the particular equipment to be properly done.