  VLBI observations of SiO masers recover at most 40-50% of the total flux
obtained by single dish observations at any spectral channel. Some previous
studies seems to indicate that, at least, part of the lost flux is divided up
into many weak components rather than in a large resolved emission area. Taking
benefit of the high sensitivity and resolution of the HSA, we investigate the
problem of the missing flux in VLBI observations of SiO maser emission at 7mm
in the AGB stars and obtain a high dynamic range map of IRC+10011. We conclude
that the missing flux is mostly contained in many very weak maser components.
