  Recent models of variations of the Sun's structure with the 11-year activity
cycle by Sofia et al (2005) predict strong non-homologous changes of the radius
of subsurface layers, due to subsurface magnetic fields and field-modulated
turbulence. According to their best model the changes of the surface radius may
be 1000 times larger than those at the depth of 5 Mm. We use f-mode oscillation
frequency data from the MDI instrument of Solar and Heliospheric Observatory
(SOHO) and measurements of the solar surface radius variations from SOHO and
ground-based observatories during solar cycle 23 (1996-2005) to put constraints
on the radius changes. The results show that the above model overestimates the
change of the radius at the surface relative to the change at 5Mm.
