The development of model equations to describe mode conversion and tunneling in an inhomogeneous plasma usually uses expansions of the Modified Bessel functions in the parameter λ=12k⊥2ρL2, keeping only the lowest possible order to demonstrate tunneling. With the high temperatures of fusion parameters, especially for fusion alpha particles, this parameter may not be small. It is shown here that the effective expansion parameter is really βj=2μ0njkTj/B02, the ratio of plasma pressure to the magnetic pressure.