Dave, you're absolutely right, the existing antenna is 1/2 wave
end-to-end, not 1/2 wave per section.

As for your other suggestions - based on other reading, it seems like
J-Poles are finicky to attach to coax. And I've looked at
phased/stacked dipoles, looks promising but I worry about the narrow
vertical beampattern.

For an elevated ground plane scenario - what's better? Radials, trimmed
to resonant length, bent down 45 degrees or so (I've read since that
this is required for 50 ohm impedance) -- or a simple ground plane, 90
degrees to the axis of the 1/4 wave whip, min. 1/2wave diameter? 900MHz
is a pretty small wavelength, I'd be fine with using a solid 6.5"
ground plane if it would get me better performance than radials.