REL Subwoofer - How to use the "Mode Selector" switch

Hi~ I hope someone can help me on how to use the "Mode Selector" switch on REL Britannia sub (mine is B2). There are four modes (1 to 4) and I was wondering which one to use if I want to reverse the phase polarity (=180) with the high level connection that REL recommends. The four modes are:

1: Line / 0 degree

2: LFE / 0 degree

3: Line / 180 degree

4: LFE / 180 degree

Many thanks!