vertical justification of fret-diagram

[Jinsong Zhao]

Hi there,

In the following snippet, I want to vertical justification of the three 
fret-diagram.

\version "2.19.15"
fret-ees =  \markup {
      \fret-diagram #"s:0.5;6-x;5-x;4-5;3-3;2-4;1-3;c:2-1-2;"
}

\relative c'' {
  \key ees \major
  bes8 ^\fret-ees ees bes ees, g4 ^\fret-ees f ^\fret-ees
}

I can do that by \tweak extra-offset #'(x . y). However, it's not easy 
to determine the exact values of x and y. Is there a convenient way to 
keep them with same base-line?

By the way, how to make the mute symbol "x" at the same line of the curve?

I appreciate you for any suggestions.

Best regards,
Jinsong