All ships have 4 arcs used to define firing angles. These angles are all 90 degrees and are measured from the center of the peg to the corners. If an attacking ship is placed with its peg exactly on the line between to arches the defender chooses which arc that applies for the purpose of modifiers.
The corners of the base or the corners of the token? The tokens aren't square, so either your front and back arcs are ~80° and the side arcs are ~100°, or you need to ignore the arcs actually printed on the tokens for checking when things are in the forward arc.