When firing, you draw a line from yellow dot to yellow dot. On the defending ship, if that line crosses the borders of their hull zone, the line of fire is blocked. Simple enough.
However, with the attacking ship, their hull zone borders continue out infinitely to form a firing arc. This means the target yellow dot will be on one side of that line or the other (or in rare circumstances, directly on it).
Ignoring the instances when the target yellow dot is on the line, this eliminates the possibility for one ship to focus fire onto one hull zone of an opposing ship. The target dot can only ever be inside one arc.
I'm not sure how I like this. I guess it will just force me to change how I approach things. I hadn't realized this implication until I actually started playing. Until that point, my goal, when possible, was to line things up so multiple hull zones can focus fire on a single zone. This is essentially impossible. Definitely changes my strategy.