Draw the vectors Paul; Best way to understand this is take it to extremes.

If we are sailing up wind (at say 45 to true) in 1 kt of wind and we are travelling at 0.5kt; this will result in the apparent wind being somewhere forward at (guess) 30 degrees. Now make the wind jump to 20kts and the wind component vs boat speed component means the apparent will move aft (the angle will increase).