what i'm wondering though is this: will the high back (higher than head
level) have an adverse effect on the sound or is it good to have a
"cushy-absorbing" surface directly behind the ears/head?

I find that the back of the chair does cause some lack of clarity.
It's a high back recliner, and the top is a little bit far back to
lean my head on comfortably, so I normally like to use a pillow with it.
I've found that using a piece of Sonex instead of a normal pillow
helps the sound. Second choice - a very small pillow that keeps my
head away from the chair back but doesn't stick out behind my ears
to reflect anything. The Sonex works better, but looks weird :-)
Hair needs to be kept back away from the ears, too. It seems that
any reflections originating very close to the ear are Not Good,
at least for me. Taking off eyeglasses makes a difference too,
although I usually don't because I tend to read and listen at the
same time. Glasses don't make a difference to "live" sounds, but
there seems to be something about the stereo illusion from two
speakers that they mess up slightly.

And to go off on a wild tangent - I wonder how much of the expectation
bias listening to new equipment comes from leaning forward an inch
or two in anticipation, and By George, it DOES sound better a little
farther from the chair back, even though it gets attributed to
some other change that was made :-)

Bob