wrote
Where is the coil on the linear monopole?

Sorry, I forgot to address this question directly. Both radiators
were base fed.

As shown at the top of that comparison page, a total of 30 ohms was included
in each NEC model to account for the loss in the connection to r-f ground,
and in the loading coil. That is why the maximum gain of both models is
about -19.5 dBi, rather than 4.77 dBi.