Alan,
On a quick skim of your post, a very nice statement of the conditions...
I would add that the "armpit" problems with a spraybar across an open venturii are all that worsen the area change, which, in turn, determines the pressure drop across the venturii minimum area.
The 'spigot' (single jet in a clean venturii) type has an advantage: It can be positioned so that the "annular fuel ring" carved into it doesn't switch from under to over the fuel level within it.
A while back, Frank Williams, as the Power Train columnist in a certain publication, ran some tests on clean venturii, and spraybar and 'spigot' configurations. ASIR, a spigot, properly positioned, drew fuel better than the others.
Frank ran several bench tests to find that oiptimum position, so, no rules of thumb from me on that...