UV_STAT handles Mosaic like Single-Field for the weighting (BEAM,
BRIGGS, TAPER and WEIGHT arguments): all visibilities are considered,
instead of those of just one among the various fields. Accordingly, the
predicted beam sizes are often underestimated compared to what UV_MAP
and FIT commands would yield.
For a fine adjustment of the beam shape and size, it is recommended to
verify using UV_MAP and FIT commands and iterate if needed.