Maybe for a house rule, on a Success + Despair while shooting at enemy engaged with your ally, your attack hits BOTH parties.
With the danger that the RAW presents on this, it's very much in the interest of characters to wait for an open shot before taking it
so I do like that about it. I do agree that it doesn't quite jibe with the concept of a "successful" check, but then it could be said that your shot was dead on...it just turned out that your ally was in the way.
In any case, the attack hitting both parties might be a good way to resolve this.