There are a few reasons why the width suggested for a BALANCE Jump saddle is usually narrower than the suggested BALANCE Dressage saddle width:
The panels on a Dressage saddle run more vertically downwards, directly underneath the pommel of the saddle and over a wider part of the horse’s body – in this way the panels support the pommel and make it sit higher in front than a Jump saddle, because the panels on a Jump saddle come much further forwards and lie over a narrower part of the horse’s body.  The panels are also often more shallow on the Jump style than on the Dressage style of the same model, so again the Jump saddle will sit wider on the horse than the Dressage of the same width.When jumping, you ride more of the time with your weight concentrated in the stirrups – this concentrates your weight at the front of the saddle, so it is important not to go too wide with a Jump saddle otherwise you risk pressure over the withers.  Having a Jump saddle too wide can affect the horse's comfort and confidence when jumping. This is because a wider saddle needs more pads under it and this increased padding can cause a very tiny delay between the moment when the horse's own weight lands over a fence and when the rider's weight in the saddle comes down onto the horse. It's only the tiniest split second, but it can matter to the horse, and many horses feel more confident with a slightly narrower saddle and minimal padding when jumping.