Ported vacuum is NEVER sourced below the throttle blades, it is ALWAYS sourced at the smallest diameter of the bore venturii, that is why, as the air flow is high there when the throttle is full open, vacuum is significantly higher there, than at or below the throttle plates.
Connect two vacuum gauges and go drive the engine around, full throttle it, idle it, and then, cruise, mild acceleration, all facets of operation. You will get the correct picture then.
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