  We present comparative studies of the orientation effect of a strong magnetic
field on the interlayer resistance of $\alpha$-(BEDT-TTF)$_2$KHg(SCN)$_4$
samples characterized by different crystal quality. We find striking
differences in their behavior which is attributed to the breakdown of the
coherent charge transport across the layers in the lower quality sample. In the
latter case, the nonoscillating magnetoresistance background is essentially a
function of only the out-of-plane field component, in contradiction to the
existing theory.
