  The boundary conditions with diagonal boundary $S$ matrix and the boundary
form factors for the Smirnov--Fateev model on a half line has been considered
in the framework of the free field representation. In contrast to the case of
the sine-Gordon model, in this case the free field representation is shown to
impose severe restrictions on the boundary $S$ matrix, so that a finite number
of solutions is only consistent with the free field realization.
