1969 F100 Fuel bowl leak down

[Redhorse1947]

I am posting this for ideas on WHY my carburetor bowl “leaks down” when the engine is HOT.
Specifics: 1969 F100 360 V8 Auto Trans (I am the original owner)
2100D 2 bbl carb manual choke (Original Carb)
Cold starting: excellent…never fails to immediately start
Hot starting: excellent if re-started within 3-4 minutes
Hot starting: poorer & poorer if re-started after 5 minutes

During the past year have installed TWO carb kits and THREE power values and the problem (leak down) continues. I can place the carb on the workbench, fill the bowl with gas and the full level remains for several days. So the problem seems to be “heat” but I simply cannot pin point the specific cause of the “leak down”. The fuel level will drop close to ½” within an hour but NEVER goes dry.

Thoughts?