Being subject to the Newtonian Law of equals and opposites even if the pair doesn't fulfil the exact symmetry (it would be lovely if it does) I think the point at which it touches the reaction line should trigger a very sharp rise. Its counterpart stopped one, took it away, therefore it should give it back. However should it break the channel, I think a very steep drop, having at least in part been responsible for halting one. Channel edges though are hard to define.