How to turn off alignment-indent after line continuation in Shell-script mode?

In Shell-script[sh] mode, Emacs defaults to this style of indentation:

/this/is/an/example/command/broken/over_multiple_lines which 
                                                       causes 
                                                       an 
                                                       annoying 
                                                       indentation

I would like to change this so that each line is indented by only a single tab further than the original line:

/this/is/another example 
  which is indented 
  by a single tab 
  shown here 
  as two spaces

This is what the relevant section of my init.el says I have customised:

 '(sh-backslash-align t)
 '(sh-basic-offset 2)
 '(sh-indent-after-continuation nil)
 '(sh-indent-for-continuation 0)
 '(sh-indentation 2))

What variable am I missing to change the alignment indent to a single-tab indent?