When I want Mia to relax on a trail, my feet go forward. I'm not bracing in the stirrups, just relaxing and letting my hips move with her back. If I want her to go fast, I let my lower leg hang down vertical from the knee, lean forward and transfer most of my weight to my thighs. With my rump barely touching the saddle, she understands it as "Go faster". If I want her to make a tight turn, I settle deep, bring my heel under my hip and get out of the way of her shoulders. She's awkward enough without me asking her for a sharp turn with my legs forward! On average, my heels are further back than I like because that is how my saddle is built, and I see no value in fighting with my saddle.
One of the things that drew me to western riding was that most people I ran in to were happy to ride their horses, and happy to let you ride yours without any lectures. I think most do what I do now - look to see if your horse is relaxed and moving cheerfully forward. If so, then how you ride is your business.
The B&W photo I posted earlier is THE western style of riding from around the 1860s thru the 1950s or 60s. If you ever watch an old western, ignore the stars sometimes and watch the wranglers riding in the background, or some of the character parts. There were a number of bit players who grew up on ranches in the 20s, 30, and 40s who can be seen riding. They are usually easy to spot, because they are moving relaxed on a relaxed horse, even when going quickly off trail.
You can ride like that old cowboy photo and not sore your horse or even annoy your horse. You can also ride in a 'dressage' position in such a way as to make your horse hate you. Or not. My horses got a lot happier when I realized (thanks, Littauer) that riding wasn't about position, but about balance and moving with your horse for whatever it is you need at that moment. Some positions work better for some purposes, so adapt what you are doing in the saddle for what you want your horse to do under the saddle.