  By strictly adhering to the microscopic theory of composite fermions (CFs)
for the Landau-level filling fractions \nu_e = p/(2 p + 1), we reproduce, with
remarkable accuracy, the surface-acoustic-wave (SAW)-based experimental results
by Willett and co-workers concerning two-dimensional electron systems with
\nu_e close to 1/2. Our results imply that the electron band mass m_b, as
distinct from the CF mass m_*, must undergo a substantial increase under the
conditions corresponding to \nu_e close to 1/2. We further establish that a
finite mean-free path \ell_0 is essential for the observed linearity of the
longitudinal conductivity \sigma_{xx}(q) as deduced from the SAW velocity
shifts.
