I don't really see why the sensors would need to be directional. It's not as if they would have been established to use lenses or paraboloid mirrors or anything.
Perhaps the display screen is holographic, and Spock sometimes doesn't bother to rotate the object to be displayed when he can tilt the whole machine instead? OTOH, perhaps all the odd rubbing is an interfacing technique specifically for rotating the object in the display, akin to Spock's handwaving in "The Cage".
Of course it could be a Spock thing even more intimately, an interfacing method only available through touch telepathy. It's well established in "The Changeling" that Spock can speak Machine with his fingers, after all.
Timo Saloniemi