Time to eat crow.
After reviewing all the posts and websites mentioned in this thread, I have decided to reverse my position on the uniflow tank. I now believe it to work as described in Nigel Frasier Ker's website. My apologies to Nigel. He was right, I was wrong.
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Now before anybody starts to gloat, let me bring you down to earth (a little). First of all, Nigel's site is not so well illustrated and it requires very close reading to truly grasp what he is saying as being true. It was only thanks to another site, referred to by Jim Thomerson that I was able to understand the physics properly. Of course then Nigel's site became understandable. This doesn't get me off the hook but I wish his graphics had included the excellent diagram from the other site which I shall attach herein for you all.
There are two forces involved in the tank. One is the pressure head force which varies with the depth of the fluid above the carb clunk. The other is the gas pressure provided by the muffler tap (and ambient atmospheric pressure).
MOST of the proponents of uniflow argued that the gas pressure from the muffler is reduced or eliminated by the depth of the pressure clunk under the fluid surface - and this is what makes the fuel flow more even - and that, as the fuel level drops, the muffler pressure transmitted is increased.
I argued that the gas pressure from the muffler tap was transmitted immediately throughout the tank with no losses.
I was right in this.
Where I was grossly wrong was in failing to understand that the two clunk locations (at the exact same depth) eliminates ANY pressure head forces, leaving only the gas pressures to act within the tank. We were arguing about the wrong forces.
Please look at the diagram and see how the "head" of pressure is NOT measured from the water surface. Now envision the vent tube being extended down a bit, to the same height as the outlet.
I hope you have all enjoyed this...
Ice man, I hate you.
(just kidding)

Allan