Inexplicable lamenesses, vices and resistances, back pain - saddle issues have many faces!
Without any doubt, the distribution of the rider's weight is an essential element when designing, fitting and checking a saddle.
The distribution of the rider's weight crucially depends on the size and shape of the panels. They must fit to the shape of the horse back. Furthermore, thinking of conventional stiff treed saddles the rock of the saddle must fit to the horse's back line. As this line changes when the horse lifts the back it is almost impossible to make this happen.
A leathertree saddle is flexible and adapts by itself while riding. This can effectively avoid hot spots which can be caused by conventional stiff treed saddles. At the same time a well-fitted leathertree saddle is strong and stable enough to avoid too much pressure under the stirrup bar which is a common problem with treeless saddles.
There are several options how to check the weight distribution. Popular because of being cheap and easy to do is the Carola pad.
A more precise assessment is possible using thermography. This method can show if an area gets more pressure than another by showing the temperature differences.