More room in a saddle seat does not mean more comfort. A seat too large leaves the rider unable to maintain a stable, centered position — constantly shifting within the seat rather than moving with the horse.
A seat too large allows the rider to slide forward into the fork or backward toward the cantle rather than sitting in the correct balanced center. This instability produces constant subtle position corrections the horse reads as inconsistent cues.
In western performance disciplines, the rider's seat is the primary communication tool. Weight shifts of as little as a pound in the correct direction communicate to a trained horse through the seat. A rider sliding within an oversized seat cannot control those weight shifts — every adjustment to stay centered is a cue the horse receives and responds to, whether intended or not.
You should be able to place a flat hand between your thigh and the front of the seat jockey with one to two inches of clearance. If you can fit more than a full hand comfortably, the seat may be too large. If the seat is too large by more than a half-inch, find a more appropriate size rather than attempting to compensate through riding technique.
David Solum has been evaluating saddle fit problems for 40+ years. Call, text, or email him directly — he can advise on whether it's a fit issue, a tree problem, or a saddle you should replace.
See also: Free Saddle Tools · How to Fit a Western Saddle · Parts of a Western Saddle · How to Buy a Certified Used Saddle