A problem on the illumination of a plane layer by a 'wide' light source and the recording of backscattered radiation by a 'narrow' - angle receiver is considered. An opaque obstacle can be inside the layer, i.e., optical properties of the medium are, in general, horizontal non-uniform. The light signal reflected from the medium with highly forward extended phase function (e.g., from a cloud) can be naturally partitioned to two components, the first arriving at the receiver from the medium in front of the target, the second - from the shadow region of the target. These components are calculated by the multicomponent approach to the radiative transfer equation, including the representation of the forward phase function as a sum of diffraction and geometrical optics terms. The computations are implemented for gamma size distribution of cloud drops. The first of the said components is analytically shown to depend weakly on microstructural parameters of the medium. The physical interpretation of such behavior of a signal, that can be regarded as a signal model for space lidar sounding, is given. The relation for the second component is also derived to show the regions of the medium providing higher sensitivity of the signal to the microstructural parameters as compared with the medium without target.