A friend who recently passed away once gave me this sketch and now, I pass it on to you. It illustrates the capacitance that a vertical antenna will exhibit at its bottom feed point versus the vertical element's dimensions.
Figure 1 A reference vertical antenna
Antenna theory is not my specialty so I have no idea who Kraus is, but if you yourself happen to know, his work is out there waiting to be studied.
By the way, for the standard rod, the exhibited capacitance comes to 9.515 pF.
Editor’s note: John D. Kraus wrote numerous text books on antennas (Amazon has some good ones here). Kraus was a US physicist who invented the helical antenna, the corner reflector and much more.