Hi, JinxedDream,
I might be new to leather craft, but I am a rider and saddles are my passion, just ask my husband.
Two different horses, different size and breed, Western, English, (jumping, dressage, all purpose), Treeless saddles, Flex Panel, I have tried them and own most of them. They ALL have their purpose.
Looking at your pictures, for the life of me I can not believe how short your fenders are. For a 36” inch inseam length, to have a leg on horse and be able to reach his barrel with heel/spur they have to be short, but they create torque in your knees.
That would explain why you don’t have that problem riding bare back.
Short fenders/leathers will also push your seat out of alignment, creating lower back problems.
And why is your Aussie Saddle more comfortable? Fenders are turned, which helps a lot, just like RufusJames mentioned.
English saddles have much thinner/narrower leathers, but with your legs, I imagine you have problems with knee blocks pushing your upper leg to outside.
I will look forward to your post on saddle making, I’m planning to make saddle pad for my daughter, with spinal protection for her horse.
Good luck, I understand saddle fitting.
Dag