Panel shims

Can affect the rider's pelvis tilt, refines the twist, and slightly deepens the seat. It goes under the front of the seat, with the wide side toward the pommel and the pointy side toward the rider. It can be moved forward/back for a greater effect.
Riders who have a low pelvic floor may not like the bolster. For those who are looking at the product to tilt the pelvis, one of the other rider balancing aids will have a great effect without discomfort.
To install, release the velcro under the front center of the seat, then tug the seat back over the front dees. Place the bolster and press the seat back into position, making sure all is still symmetrical. Replace the front velcro tab and push the seat back over the front dees. This last part can be difficult, especially when the saddle is new - to make it easier, pull some twine or a shoelace through the dee to give you more leverage.

If panel shims aren't enough or you have closed panels, it's also possible to shim in the pads (although the pocket shims for close panels may be a better option for both cases). You want to make sure you are still using the foam pad inserts so you don't put a transition next to the horse, plus they'll stay in place better.
One advantage of the pad shims is that they are easy to put in place while the saddle is on the horse (not girthed) and can easily be removed if one horse needs shims and another does not.

Wedged shim inserted between base and closed panels. Perfect for those who want the classy look of the closed panels (especially with a matching color/material) but need a little lift in front to balance the rider for horses who might be downhill where the saddle wants to side or who have less curvature than the Ghost base. These work great with velcro opening panels too, and sometimes are a bigger solution than the felt shims that can go inside the panel. This is also the best balancing solution for the western saddle. Sold in pairs.

For those who want a cheaper option or more ability to customize, I've made some less polished seat reducers from wool felt. And here's a hint - if you have similar material laying around, you can make your own or even do other customizations to the fit of your saddle.
These are made from 1/4" thick each and can be used with 1-3 (maybe 4 if you adjust the position of your seat back on the base). Typical use is 2-3 for ~1/2" to 3/4" smaller seat