The recommendation to use 6 (rather than 4) scans is
(a) to ensure that sufficient uncontaminated samples are available at
taken at each spectral point and (b) to allow median filtering.
For 
s integration ramps (used for all but very bright sources (see
point 3), this implies Tint per sample must be at least 2.4s.
This is the observing strategy currently being used by the LWS Consortium.