How many progression holes?

[gr_diver]

Today I realized that my 2 (vacuum secondary) Solexes are not 100% identical as I thought!

The one that was originally on the engine has 3 progression holes, but another I have bought (and I currently use) that came of a same car with the same engine has 2 progression holes.

Why would there be this difference? In theory, which would feed better at the range that progression operates? I cannot measure port sizes due to lack of tools, but the ports on the one with the 2 look slightly larger.

Since a year ago that I fixed my leaky power valve on my old carb I have been fighting a hesitation issue at part throttle. The "new" carb improved but not solved the issue, and now I found this. (the power valves on both work now as they should, the leaky one was just covering the real problem and gave nice puffs of black smoke at acceleration...)

Should I begin to think that there is a "problem" with the old (3 port progression) carb, and a good working but insufficient (progression) new carb? But I can't understand why would there be a difference? They are both the latter 7 screw air-horn.