  We present results of a study of the fast timing variability of the magnetic
cataclysmic variable (mCV) EX Hya. It was previously shown that one may expect
the rapid flux variability of mCVs to be smeared out at timescales shorter than
the cooling time of hot plasma in the post shock region of the accretion
curtain near the WD surface. Estimates of the cooling time and the mass
accretion rate, thus provide us with a tool to measure the density of the
post-shock plasma and the cross-sectional area of the accretion funnel at the
WD surface. We have probed the high frequencies in the aperiodic noise of one
of the brightest mCV EX Hya with the help of optical telescopes, namely SALT
and the SAAO 1.9m telescope. We place upper limits on the plasma cooling
timescale $\tau<$0.3 sec, on the fractional area of the accretion curtain
footprint $f<1.6\times10^{-4}$, and a lower limit on the specific mass
accretion rate $\dot{M}/A \gtrsim $3 g/sec/cm$^{-2}$. We show that measurements
of accretion column footprints via eclipse mapping highly overestimate their
areas. We deduce a value of $\Delta r/r \lesssim 10^{-3}$ as an upper limit to
the penetration depth of the accretion disc plasma at the boundary of the
magnetosphere.
