  We present the results of our recent systematic study of the light-cone
expansion of heavy-to-light transition form factors in a model with scalar
constituents [1]. We show that the higher-twist contributions (represented in
this model by off-light-cone effects) all have the same behaviour in the 1/m_Q
expansion. The suppression parameter of the higher-twist contributions compared
to the lower-twist contributions is, in general, the inverse Borel parameter
\beta. The only exception here is the case of the leading and the subleading
twists: they are of the same order in 1/\beta because of an extra suppression
of the leading-twist contribution to the form factor.
