John,
I have a 12cm reach Tallux for the Wavie on my 64 Atlantis. With that stem, the bar ends don't quite come back as far as the back (saddle) side of the vertical part of the stem.
When I was deciding on the stem reach for the Wavie, I knew I wanted a slightly more aggressive position. I have Brooks B17 Imperial saddles on all of my bikes...and I know the distance between the saddle nose and a straight line connecting the two bar ends for a more aggressive, and a moderately aggressive position. So, given the sweep back of the bar in question, and level of aggressiveness I'm after, I just deduce the required stem reach to get that saddle nose to bar end distance I'm after. Works for me.
Tom