concentrate is inconsistent

[ellson]

Edge concentration is inconsistent in behavior in dot. in the following graph, why is "{a b} -> d" concentrated, but "{A B} -> D" not?

digraph G { concentrate=true a -> b -> c -> d { a b } -> d { A B } -> D }

What I'm really looking for is a way to represent netlists in dot. Concentrate almost handles 1-to-many netlists, but not quite.

It looks like concentrate might use a zero-sized floating node for the branch point? Can this type of node be exposed in the dot language? And can it be allowed to position half-way between ranks so that "{A B} -> D" will concentrate?