Ok, I am sold in squandering $1K on a Garmin Panoptix plus a Multi Function Display after a lot of research.

I see the difference between P21-TR vs, P21-TM as follows:
​(1). trolling motor mount vs. Transom mount
​(2). Power cable and Ethernet cable (13 feet vs. 30 feet)
​(3). Beam width (45 degrees by 90 degrees vs. 20 degrees by 90 degrees)

​(1) and (2) are obvious, but (3)??? can anyone help explain this please?

Q1: What are the 2 degrees?
Q2: Is 45 a wider angle cone than the 20? so 45 can cover more water than the 20?

I do mostly shallow water fishing under 60 feet, so I am thinking P21-TR will work better than P21-TM if TR covers more water (wider).