afaik
the tensile load will determine whether the small end eye can be designed for strength only ....
or whether stiffness (to avoid excessive contact loadings from pinch of the small end bearing) is the dominant design factor
Wright's Cyclone 18 c.1941 seems to have been a pioneer of H section rods
but maybe that was for the master rod only (and for master rod specific reasons)
or was it said that there some reason, from gas load distribution ?