Peter Duniho wrote:

Is there an altitude above the ridge line at which the "mountain wave"
effect isn't significant?

There's no reason to be afraid of wave. Wave isn't turbulent at all,
just think of it as a region with strong up or down draft. Stron means
just that: strong. You'll see 20 fpm and more.

No way to fight a downdraft of 20 fpm. So don't fight it, rather fly
perpendicularly to the ridge until you leave that region. Chances are,
you'll find a region with the same amount of updraft there. Throttle
back and enjoy.

Rotors are a completely different story, but you won't encounter them
above the peaks. Of course you may hit some other turbulence, so stay
below the yellow arc.

Stefan