rule of thumb
I use a similar rule of thumb.
I go to one of the dish aiming calculators and input my location.
The satellite at your same longitude will be the highest one in the sky.
That's the one with the highest elevation.
As you go east or west of that satellite, they all get lower in the sky.
Any satellite about 20° elevation or more, should be easy to receive (assuming no threes, buildings, mountains in the way).
Satellites down to maybe 10° elevation will be tricky, but possible to receive.
Any bird below 0° elevation will be totally impossible to hit.
A good fringe example, would be folks living on the east coast of the USA.
Shooting over water, they could possibly catch a satellite down to a couple of degrees above the horizon, since they are looking across a flat terrain.
Another consideration is this:
To the observer (that's you), satellites 2° apart, located high in the sky, appear farther apart.
As you choose satellites down to your east or west, they appear closer together.
So, being able to pick out one bird of many, close to the horizon, may become difficult.
A larger dish with sharper aiming may be helpful.
Most motorized systems cannot accurately aim your dish as you get close to the ends of travel (east or west limits).