Cecil Moore wrote ..
Since the monopole is purely resistive around 1/4WL and
around 1/2WL, i.e. the reactance is zero at those two
points, it is simply impossible for it to be be any
other way.

That's very true, but between the 1/4WL and 1/2WL zero-reactance
points, reactance increases with frequency, peaks, and then begins to
decrease to cross zero again at the 1/2WL point. This peak is NOT
half-way between 1/4WL and 1/2WL, but skewed heavily toward the 1/2WL
point. My question is what determines where that peak occurs?

Can the reactance peak be somehow adjusted (frequency position, not
magnitude) for tuning purposes? Magnitude is easily adjusted by simply
adding inductive or capacitive reactance, which doesn't change the
shape or peak position of the reactance curve, but simply moves the
curve up or down to change the points at which it crosses zero
(resonance frequency). Controlling the reactance peak position could
do the same.

The answer may be simple and common knowledge, but I haven't found it.

Al