  The location of the cutoff in the gravitational-wave spectrum of black
hole-neutron star mergers is correlated strongly with the neutron-star radius
for the case that the neutron star is disrupted by the black hole during the
merger. However, the modulation which appears in the spectrum due to the mode
mixing makes it difficult to measure the cutoff frequency if gravitational
waves are observed from inclined direction or the binary is precessing. In this
letter, we show that the cutoff frequency can be measured even in such
situations with a method we have recently proposed to reconstruct the face-on
waveforms only from the strain observed from a particular direction. We show
that the systematic error in the measurement of the neutron-star radius can be
reduced to $\lesssim 5\%$ for the case that tidal disruption of the neutron
star occurs significantly.
