Shortening ties

[Michael J Millett]

I have been attempting to get ties to stop short of the final notehead, 
but have been unsuccessful after several days of trying.  So I now have 
to ask for help.

 I am attempting to get the ties of a chord to stop well short of the 
second note.

Logic dictates, to me at least, that one of these should work:

\once\override Tie #'X-extent = #'(-10 . -10) <b,, b,,, >4--~

\once\override Staff.Tie #'X-extent = #'(-10 . -10) < b,, b,,, >4--~

\once\override Voice.Tie #'X-extent = #'(-10 . -10) < b,, b,,, >4--~

But they don't. I am not getting error messages, but the ties are not 
moving, either.

Thanks for any help you can provide.

Michael