The effects of different radial distributions of basilar membrane velocity on the fluid coupling in the cochlea are studied. Different mode shapes across the width of the basilar membrane, modeled as a beam, are simulated by assuming various boundary conditions. The results suggest that the fluid coupling is insensitive to the resulting differences in mode shape. This validates the assumption commonly made in cochlear models that the fluid coupling can be reasonably well predicted by assuming a single modal shape across the basilar membrane width, even if the exact form of the radial profile is not known.