I have used this elastic foot three times for making bathing suits.  The stretch of the elastic only works when set on "4".  Anything less does not stretch the elastic for application.  This may be due to the knit elastic that I am using.  Fortunately, the setting "4" seems to be just the right amount of stretch I need.  I see myself just doing it with the regular foot and stretching the fabric and elastic if I need a tighter fit.