I found this datasheet on bicone antennas, that is a useful reference for seeing the relationship between bicone dimensions and bandwidth.  From these it looks like the lower end of the band is at about f_low=c/(4*L_E), where L_E is the entire length of the antenna (twice the length of one cone), although we'd expect the peak gain to be where a quarter wavelength is just one of the cones (and the figure may roughly support that).

The attached file comes from this website:

https://www.ramayes.com/Biconical_Antennas.htm