I'm with the TBS on this one. I normally just do two passes on my neck, basically, up, and down, no sideways, If I get BBS, great, if not. I don't sweat it. I'm going for comfort, as well as BBS. I have to be careful on my neck, it's very sensitive and subject to irritation. I have be aware of the contours, and the blade angle.
Good Luck....