  We consider a class of Hermitian Hamiltonians with position-dependent mass
$H=((m^alpha)p(m^beta)p(m^alpha))/2+\V$ with $2(alpha)+\beta=-1$. We apply
these Hamiltonians to different piecewise flat potentials and masses (step,
barrier, well and multibarrier). To raise the ordering ambiguity we impose that
the transmission coefficient tends to the unity as the energy increases
indefinitely. We arrive at the conclusion that the form
$H_flat=(m^(-1/4)pm^(-1/2)pm^(-1/4))/2+\V$ of the effective Hamiltonian is the
most adequate to describe such flat potentials and masses systems.
