S，H, L

S/L and H/L is for correcting low angle peak asymmetry.

H is the detector slit length. L is the detector to sample distance. S is the widths of illuminated sample.

The typical value is in the range of 0.005 to 0.020. You may have to try and test. 

reference:

http://journals.iucr.org/j/issues/1994/06/00/hn0025/hn0025.pdf