[Xy-pic] arrows passing object bounds in xymatrix

[Willem Heijltjes]

Dear all,

I've been using the archives of this list to solve my XY-troubles for
some time now, but this is the first time I can't seem to find a
solution. The problem is this: I have a lot of xy-matrix diagrams to
draw, and I'm using macro's to make life easier. These are forcing me
to use \POS or \drop, as * does not get expanded all the time. But
objects dropped this way don't override the size set by entry
modifiers, at least when used as the target of an arrow. See the
following example.

\xymatrix @!0 @C=32pt @R=16pt @*=<0pt> {
  *=<10pt>[o][F]{} \ar@{-}[r] & *=<10pt>[o][F]{} \\
  {}\POS*=<10pt>[o][F]{} \ar@{-}[r] & {}\POS*=<10pt>[o][F]{} \\
}

Has anyone encountered this before, and is there a solution? The way I
address it now is by dropping an extra object, using *, but this is
rather cumbersome.

Many thanks,

-Willem