Matt,
That needs to include a picture of what your transducers ‘sees’ to its left side, so you need to take the picture at the same height as the transducer from the right side of the transom. What you described sure sounds like there is some sort of obstruction to the upper part of the left Si sonar beam.
Are you sure that the left side does not clear up when the boat os drifting and the motor is trimmed up all the way?
Any chance that you could test your Si unit on another boat that is running a Humminbird Si sonar unit? Also try and test one on your boat as well. Just connect the power cable and transducer for this testing. Any model Humminbird Si unit will work for this testing.