60 Degrees?

[DigitalAura]

From the Sub Handbook in the sticky:

95. When attacking ships with low and medium speeds, at close range, it ballistically advantageous to fire at an angle of the target of 90, as errors estimating the position will in this case have the least effect, besides which the speed of the enemy can be most accurately gauged in this position. If the range is longer (over 1,000 m), and the target is traveling at a high rate of speed, an attempt should be made to launch the torpedo at a smaller angle, say, 60.

Can someone tell me why a smaller angle is recommended here?
And if the enemy is to port is that 60 degrees off the port or the starboard?