Matt's advice makes a lot of sense, but he is leaving a key component out. He has years and years of hard trail experience. So in some cases hard trail runners assume, we non-trail runners
know what is rattling around in their heads for stuff they now take for granted ?
He knows that trail like the back of his hand, in fact he probably calls out every rock and root by names he has given them over the years ?
Me on the other hand, trip over pebbles on a flat pavement race, let alone going downhill at 13% grade!
I'm pretty much a trailing foot dragger not a stepper. 90 percent of the time it's not the lead foot
that gets me in trouble, it the trailing foot. My trail foot is like a pack bungee cords. it only hooks stuff you don't want it too ?
I proved that to myself, by looking at the top toe box of the brand new, only had 20 miles on them, running shoes that I ran in for PPM. There were so many cuts, scrapes, and scuffs on the toe
box that I swore those shoes had 400 miles on them when done. This meant I had to get my trail foot even higher because I wasn't perpendicular to the trail, which meant I was leaning back.
So yes, Matt's assessment of running perpendicular to the trail is correct, but that also means, you will be going much faster than I felt comfortable with, especially on an un-familiar trail.
I ran trails in my area twice a week which has roots and rocks to run on and step over, so I thought I had a good handle on it, But the PPM trail was a "Are you kidding me trail ?"
I'll admit it, "Hi, my name is Chuck, I am a downhill trail wimp". I'm glad I had enough sense to enjoy the PPM run, and not try to race it for a better time!
Enjoy the run, and good luck !