Mounting any xducer directly to the side of a SI xducer can partially block the SI beam on the obstruction side ...

This scenario is more pertinent if the SI xducer is HB (HB SI beam reaches all the way to the water's surface above horizontal from the SI xducer housing) ...

This can be avoided by mounting the 2nd xducer a little higher than the SI xducer ... or 1 xducer in front of the other ...

Rickie