How to prevent Graphviz from moving nodes to accomodate an edge - graphviz

Question

I'm trying to reproduce the following figure using Graphviz:
Here's what I came up with so far:
digraph
{
rankdir="LR";
splines=polyline;
b [shape=circle, label="", style=filled, color=gray, width=0.2, height=0.2];
c [shape=box, label="C(s)", style=filled, color=gray, xlabel=controller];
d [shape=box, label="P(s)", style=filled, color=gray, xlabel=plant];
a [shape=point, color=transparent, label="a"];
e [shape=point, color=transparent, label="e"];
f [shape=point, color=transparent, label="f"];
c -> d [label="u"]
b -> c [label="e"]
a -> b [label="r"]
d -> e [dir=none]
e -> f [label="y"]
e -> b
}
This gets me close but not quite there yet, as dot seems to move the nodes to accomodate the edge from e to b and not the other way round:
How do I get it so that the edge from e to b bends around the nodes rather than displacing them?

Answer 1

(lots of trial-and-error)
used html records to contrail external label positioning
constraint=false & dir=back for e->b edge
turned off edge clipping as needed to improve edges
digraph {
// lines were rearranged just to simplify my comprehension
rankdir="LR";
splines=polyline;
//splines=ortho; // might work, if edges use xlabels
a [shape=point, color=transparent, label="a"];
b [shape=circle, label="", style=filled, fillcolor=gray, width=0.2, height=0.2];
// c & d use html tables to better position exterior labels
c [shape=plaintext label=<<TABLE BORDER="0" >
<TR> <TD>controller</TD> </TR>
<TR> <TD border="1" port="p0" bgcolor="grey">C(s)</TD> </TR>
</TABLE>>];
d [shape=plaintext label=<<TABLE BORDER="0">
<TR> <TD>plant</TD> </TR>
<TR> <TD border="1" port="p0" bgcolor="grey">C(s)</TD> </TR>
</TABLE>>];
e [shape=point width=.01 label=""];
f [shape=point width=.00 label="" color=white];
a -> b [label="r"]
b -> c:p0 [label="e"]
c:p0:e -> d:p0:w [label="u"]
d:p0 -> e [dir=none headclip=false]
e -> f [label="y" tailclip=false headclip=false]
b -> e [dir=back constraint=false]
}
Giving:

Answer 2

Based on the above, wouldn't changing:
e -> b
into
e -> b [dir=none constraint=false]
i.e.
digraph
{
rankdir="LR";
splines=polyline;
b [shape=circle, label="", style=filled, color=gray, width=0.2, height=0.2];
c [shape=box, label="C(s)", style=filled, color=gray, xlabel=controller];
d [shape=box, label="P(s)", style=filled, color=gray, xlabel=plant];
a [shape=point, color=transparent, label="a"];
e [shape=point, color=transparent, label="e"];
f [shape=point, color=transparent, label="f"];
c -> d [label="u"]
b -> c [label="e"]
a -> b [label="r"]
d -> e [dir=none]
e -> f [label="y"]
e -> b [dir=none constraint=false]
}
as on: http://www.webgraphviz.com/
I get:
(Disadvantage we still have a small gap at the line labeled y).