  We describe a combined dynamic atmosphere and maser propagation model of SiO
maser emission in Mira variables. This model rectifies many of the defects of
an earlier model of this type, particularly in relation to the infra-red (IR)
radiation field generated by dust and various wavelength-dependent, optically
thick layers. Modelled masers form in rings with radii consistent with those
found in VLBI observations and with earlier models. This agreement requires the
adoption of a radio photosphere of radius approximately twice that of the
stellar photosphere, in agreement with observations. A radio photosphere of
this size renders invisible certain maser sites with high amplification at low
radii, and conceals high-velocity shocks, which are absent in radio continuum
observations. The SiO masers are brightest at an optical phase of 0.1 to 0.25,
which is consistent with observed phase-lags. Dust can have both mild and
profound effects on the maser emission. Maser rings, a shock and the optically
thick layer in the SiO pumping band at 8.13\micron appear to be closely
associated in three out of four phase samples.
