Actually I wasn't really commenting on the rudder area, more the whole design of it.

Having (this is my understanding) a lot of area above the trustline will translate into an uneven amount of lateral (trasnlated in knife edge to up-down) force about the centreline. much like having only one elevator. This in turn would lead to roll coupling in K/E and the sweep back may also add to increased elevator coupling, as the forces for the root are closer to the cg and the tip is further away.

Just a thought. I know That a lot of the old rudder only designs had massive sweep on the rudder to add a little but of "up elevator" effect on kicking the rudder, I'd assume that the shrike rudder would do the same.