Sometimes changing the stirrup length can help. The holes in the western saddle are just a basic setting. There's no law says you can't punch holes halfway between. That little difference might make a big difference. A side note: the Blevins quick adjust buckle is what contributes to having a very stiff stirrup leather. For many years, because a cowboy didn't loan his saddle, the leathers were laced which allowed the leathers to be more flexible. I cut them off one saddle and changed to lacing and haven't looked back. The Blevins were great for riding stables, dude ranches, etc.
I looked at that crooked stirrup link,,, what a joke, might be the best stirrups in the world but the picture is laughable.
"Normal" stirrups never set like that unless they are a mile too long. If you need to resort to BS pictures like that to sell a product, I figure your product is junk.
Unless your leg hangs straight down, as in completely relaxed, that is the only time the bottom of your stirrup would be parallel to the ground. When one is riding the lower leg is angled away from the horse to not make constant contact. Thus the bottom of the stirrup should follow that angle in a straight line from knee thro the foot. In order that it remained parallel to the ground, the rider's ankle would have to roll the foot inward to maintain the contact.