A simple way of checking saddle fit is the "pill box" method. Take a medication container ( cylinder shape ) and place it on the seat of your saddle while it is on your horse with no pad. Where the med container comes to rest is your balance point, it may be too far forward or back. Now take the pad and place it on your horse with the saddle on the pad, if the bottle stays in the same place or moves take note. Remeber a pad is not always the answer to an unbalanced saddle, your horse may need a chiropractor and a visit from the saddle fitter.
Another great observation to make is the shoulder symmetry which changes saddle fit. Draw a chaulk line from the back of the shoulder blades ( scapula) up to the spine. Stand on a box behind your horse w hands on the butt and a friend holding the neck and head straight. Observe if the lines meet or is one forward to the other. Any uneven lines will make the saddle twist and cause pressure points. A chiropractic visit , or farrier,and or massage should be considered before u get a pad or change saddles.