I don't know of a way to do this simply with a symbol. What you're doing makes sense for +, it could get bad pretty fast with other symbols. If you use custom marks such as imported icons or images you generally want the proportions to be constrained.
If just limiting the width would be sufficient (so there is no overlap between states) you could drag another copy of state on the columns shelf (you can create a duplicate copy of the state dimension for this if you'd like to hide one of them). For small marks, you may still see a difference in the horizontal, but if all the marks are longer than the column it should work.
The next thing I'd start to think about is a dual axis graph, tackling the vertical and horizontal segments individually, or maybe a polygon plot. Either would be more complex, and potentially introduce other issues, so I'm hoping duplicating state does the trick.