the saddle you have on your arab is not likely a semi qh bars. A semi is designed more for a horse WITH withers. what you have is more likely a full qh, or even an arab tree. I am making a huge guess on this, but I only say this because arabs are often "mutton withered", meaning low withers and high shoulders, requiring a rather wide tree in the front, but a relatively vertical alignment of the bars.
Now, I am not pro. this is based on my limited experience. so, gather that with other folks experience, and you'd widen your knowledge base.