If find it seems about right in practice - and so far no one has complained or even commented.
I did a few experiments to see what felt comfortable, and found bottom of the TV at about or a little bit above eyeline worked well. Especially as I wear varifocals these days. I find I can also comfortably rest my head on the couch (which reclines) and still watch the TV out of the distance part of my glasses.
There are two centre speakers - a smaller Yamaha NS-C110 which gives very good voice clarity below the screen, then a larger Paradigm CC-350 above the screen which adds some extra "punch" and better matches the sonic quality of the TDL RTL3 main speakers, so sounds that pan side to side don't change timbre as they cress the centre. They are both hidden behind a light weight frame made from some strips of ply, pocket screwed together, with acoustic speaker cloth stretched and glued over it.
Probably makes more sense if you look toward the end of the full build article: