Al, WA4GKO wrote:
"---when it`s too short for resonance, reactance is capacitive, and is
inductive if too long."

Thats exactly correct for an open circuit dipole or monopole, but folded
elements are backwards because they operate like loops and shorted
transmission lines.

Kraus says:
"Consider a two-wire folded dipole shown in Fig. 14-27a. The terminal
resistance is approximately 300 ohms. By modifying the dipole to the
general form shown in Fig. 14-27b, a wide range of terminal resistances
can be obtained, depending on the value of D. This arrangement is called
a T-match antenna."

The ARRL Antenna Book says:
See Fig 9. Each such T conductor and associated antenna conductor can be
looked upon as a section of transmission line shorted at the end. (This
is also true of the short folded monopole.) Because it is shorter than
1/4-wave it has inductive (Not Capacitive) reactance. As a consequence,
if the antenna itself is exactly resonant at the operating frequency,
the input impedance must be tuned out if a good match to the
transmission line is to be obtained. This can be done either by
shortening the antenna to obtain a value of capacitive reactance (The
T-match antenna itself is open-ended) at the input terminals, or by
inserting a capacitance of the proper value in series at the input
terminals as shown in Fig. 10A."

The too-short T-match has excess inductance to be cancelled just as does
a too-small loop or folded antenna. This is accomplished by adding
capacitive reactance. This is the opposite of your short mobile whip
which needs a coil.

Best regards, Richard Harrison, KB5WZI