Tame quivers, semi-invariants, and complete intersections

Let Q be a tame connected quiver and d a prehomogeneous dimension vector for Q. Then the set of common zeros of all non-constant semi-invariants for d-dimensional representations of Q is not too far from being a complete intersection. In fact, there is a bound 4 on the difference between the number of generators for an ideal defining the zero set and its codimension.