I am intensely interested in upgrading to a side imaging unit, but I fail to see how side imageing can not be greatly attemuated or just completely blocked by the outboard motor on the side opposite where the transducer is mounted on the transom. Please enlighten me.

It's simple, you position the SI transducer and/or the outboard so that one side of SI is not blocked.
To get more clearance a jackplate helps, but otherwise you trim out the outboard when at idle speed scanning to get the clearance.

I have the Humminbird MEGA SI+ transducer that is 8 1/2" long attached under the transom step to get the clearance without excessive trim-out.



When I had an ONIX HDSI transducer, I did the same thing with the Transducer Shield and Saver mount:

When there is a jackplate, solutions such as this are very popular: Russell Marine Mounting Bracket

My Ranger has a sizable "step" in the hull behind the actual pad of the boat, similar to the prior post's photo but larger in size. My original side-scan transducer was mounted there.

When you are actually going slow enough to use it just trim your motor up enough so it can read the other side.

Installed correctly , the transducer is shooting between hull and motor,. as mentioned above , if the motor is blocking signal , trim up a bit

Mo