The right saddle: what to consider.
Think about a young horse in the beginning of his training:
the back muscles are not as developed as in an adult horse, so the rider has to choose a saddle that fits to the structure of the horse at that moment.
After some months of training, the young horse changes its structure, increasing muscle; it's easy to understand that the saddle we are using is not the correct one: the tree size, the inclination of the panels, are inappropriate.
It would be a big mistake try to solve the problem with extra padding. It would be like groped to alleviate the pain of a too tight shoe with a pair of very thick socks. If we increase the thickness of the padding the shoe will be even tighter.
The same happens with the saddle: if it doesn't fit will be a torture for the horse and if we add padding the problem will be more serious. It is important to consider that increasing the padding can penalize the position of the rider and cause a loss of contact with the horse.
This example is not only for young horses, but also for adult horses that restart the training after a rest period, or all the horses that are changing their shape with the traininig.