Actually, a lot of it depends on who makes the saddle. A lot of the cheap imports are really way off. A friend bought a saddle off of Ebay that had semi-quarter horse bars. Didn't fit her horse becuase it was too narrow. She sent the saddle back and got the same model with full QH bars. Same problem. Go figure.
And to make things more confusing - the angle of the bars by one manufacturer, either semi, QH or full QH, will be different from the angle of another manufacturer. So, just because a Simco saddle with semi QH bars fits your horse just fine, doesn't mean that a Circle Y saddle with semi QH bars will fit the same way.
If I could find a saddle fitter around here, I would certainly pay them a visit. However, there aren't any - even though the Billy Cook factory is less than an hour from my house.
My mare is proving to be a real PITA to fit!