REL Subwoofers help

Hi,

I am dialing two REL S5/SHO subwoofers and am curiours about the crossover.  The instructions say most systems will be about 15 clicks from lowest setting (give or take 3 clicks).  The range on the knob on back of REL is 30hz to 120hz.  Does that mean if you go halfway its 75hz.  If that is true then seems strange that the recommended crossover is somewhere 52.5hz to 70hz.  

The above if true seems strange because my speaker crossover is 35hz +-3 hz.  So wouldnt it seem that the crossover should be at roughly 38hz?  But if you set at roughly 38hz the subwoofer is barely kicking in.  

I must be missing something......soundwise the 15clicks seems to be about right but I just want to understand where I am roughly setting the crossover