Very good point.
I picked the closest anchor to the load take off point. Why? Because I didn't have a control line over 200 feet.
We decided later that the control line, (belay line) really wasn't holding much weight and stepped down a size in rope so it wasn't so heavy to haul back, we had to add a short section of rope to the end to make it long enough though.
There was a little old stump directly in line with the speed-line that they guys later put a snatch block on and used it. They spotted it and made a smart move. Now, I recall, they put a block on that little stump and ran it over to the LD if they needed a wrap. Small loads, they could just hold by hand and run it through that block on the stump.
Also, shortly after the load went down the speed-line in the picture of mine that you showed, the belay line wasn't pulling down on the speedline anymore. Every so slightly to the side maybe, but I never noticed the speedline being pulled.
But you are absulutely right, if one wanted the perfect set-up, with the least amount of load on the speedline, it would be best to have the belay line right with the speedline and start where it does.
Maybe even the belay line above the speedline, but then you'd probably have problems rubbing the belay line against the speed-line.
Thanks for the intelligent post!