Pedal type and foot placement and orientation

Speaking to the low heels flat pedal position. That's to keep you from being bounced of your pedals when going through bumps/rocks/roots and cornering. Plus you benefit from putting your weight on the pedals. And, of course, you're not pedaling at this time.
Low heels is not done on smooth ground or when pedaling.
This allows you to use stubby short pin pedals instead of the longer sharper pin versions.
Shoes can be running or trail shoes with some lug pattern. The low heels creates an angle affect interface between the pins and the sole of your shoe. You'd have to scrape the pins through the tread. Impossible if weighted. You can't come off.
This combo doesn't cut up your shins or need shin guard protection.
I use Adidas Boost midsole shoes because the Boost midsole greatly reduces vibration transmission into your foot. Otherwise I'd get numb after a couple hours of rocky trails.

Longer sharp pins and 5.10 type sticky rubber sole shoes works good for downhill seated riding without as much weight on the pedals. The sharp pin versions can't be used with running shoes because the pins destroy your soles.

I physically can't drop my rear heel. I'm not that flexible. Best I can get is rougly horizontal with my rear heel, which is fine. The leading heel dropped is what matters most when coasting through chunk/chatter. Pointing your rear toe down and dropping your front heel gives you the "bowl technique" that'll give you really solid attachment to the bike (esp used when the bike leaves the ground).

Honestly, you should be able to drop your heels when using clipless pedals, too. No, you're not going to do it when you're actively pedaling. But because dropping your heels lowers your center of mass, it benefits you with clipless pedals, too.

I had a pro fitter adjust my clipless setup on my road bike to give me as much of a midfoot placement as the shoes allowed. He probably would have gone farther if the shoes allowed more adjustment. I really liked that a lot better than putting the cleat right at the ball of my foot. Part of the foot placement difference has to do with how your foot is supported by the pedal. With a platform pedal/flat shoe combo, you support your foot better with a more midfoot placement. Roadie clipless supports your feet quite a bit differently compared to mtb clipless.