Yeah, the cone angle is "set" in the transducer, though some units may have settings where you can switch from one angle to another.

Check this out for a better understanding of the coverage area of 2d sonar cone :




And like Bricks says ... you don't really have any idea of the direction of the fish showing on the screen. The transducer can only pick up the object within the cone (& maybe a little outside of it) and it can only tell you how far away the object is from the transducer & NOT always the actual depth of the object.