  We measure the Einstein radius of the single-lens microlensing event
KMT-2022-BLG-2397 to be theta_E=24.8 +- 3.6 uas, placing it at the upper shore
of the Einstein Desert, 9 < theta_E / uas < 25, between free-floating planets
(FFPs) and bulge brown dwarfs (BDs). In contrast to the six BD (25 < theta_E <
50) events presented by Gould+22, which all had giant-star source stars,
KMT-2022-BLG-2397 has a dwarf-star source, with angular radius theta_* ~ 0.9
uas. This prompts us to study the relative utility of dwarf and giant sources
for characterizing FFPs and BDs from finite-source point-lens (FSPL)
microlensing events. We find `dwarfs' (including main-sequence stars and
subgiants) are likely to yield twice as many theta_E measurements for BDs and a
comparable (but more difficult to quantify) improvement for FFPs. We show that
neither current nor planned experiments will yield complete mass measurements
of isolated bulge BDs, nor will any other planned experiment yield as many
theta_E measurements for these objects as KMT. Thus, the currently anticipated
10-year KMT survey will remain the best way to study bulge BDs for several
decades to come.
