The thing being pointed at is the RX, the blue thing is a servo.
You can mount a servo anywhere you like, in any attitude. The servo doesn't care. On the cenreline is only favoured because there is least weight balance problem, and the steering linkage setup is simplest to figure out. As a rule, both the tiller arm and servo arm, at rudder centered and TX stick centred, should be at right angles to a line drawn through their respective pivots, and preferably on the same side. This gives an equal response both sides.
Although the servo can be shoved round through 200+ degrees, when controlled by the radio, you get about 45 deg each side, the mechanical stop inside the servo is to prevent the servo destroying the position sensing pot.