A slight tilting of the ceilometer gives  better performance in rain.

Rain drops tend to flatten as they fall.  See the NASA explanation for this 

Consequently, when aligned vertically the backscatter from raindrops may be sufficiently high to cause difficult in resolving the cloud base above the rain.

However when tilted, the backscatter of laser pulses by the raindrops is reduced .

In heavy rain even a tilted ceilometer cannot resolve the cloud base since the integrated backscatter quickly dominates and prevents further penetration up to the cloudbase,  while extinction in the return path also starts to extinguish the return signal..

Please refer to the screen below.

These tests were carried out during light rain.  The tilted unit shows resolvable cloud base while the untilted unit reverts to vertical visibility.

The 8200-CHS has the capability of detecting up to 4 simultaneous layers but certain types of standard messages display only 3 layers .

If the lowest layer is optically dense,  the returns from beyond the first  layer are extinguished ,  and the layers above it are not detected until a gap in the lower layer is detected.   If the cloud is not optically dense,  the return from a higher level cloud is not significantly attenuated when passing back through the lower layer,  so both layers can be detected.

Here is a case where multiple layers are  at 6620 and 7290 are both detected.