Avoiding the trails can generally explained in fairly simple ways; trail lets in more sunlight so ground near the trail is drier, soil of trails are often heavily compacted which means very dry and hard with very wet and soft on either side from rain water run off, trails funnel air flow down them which affects the moisture levels in the air and soil, etc. The thing here is their knack for growing out of sight of the trail, which is not just a distance thing, many mushrooms are far from inconspicuous and can be seen from a good distance but seem to be able to find those places where they won't be noticed even when growing near a trail.

So you look at a particular mushroom's requirements for fruiting and look to see how those are met by the place they are growing and try and try to figure out why they fruited in just that spot but not 5 feet over offers the exact same conditions other than that spot 5 feet over being more visible from the trail. On the larger well traveled trails it is fairly easy to find possible explanations, that spot which is not visible from the trail is often the spot protected from how the trail affects airflow/sunlight but things get less clear on the small less traveled trails which have a minimal affect on the local environment.

You can generally explain away everything with simple biological responses but often it requires quite a few and their all being informed by the others, not just acting in isolation, and at that point it starts looking like some level of intelligence. I am always amazed by the number and variety of mushrooms you find once you leave the trail and you don't even have to go far, 5 or 10 feet is often all it takes.

Unlikely I will ever do any sort of field study, I am perfectly content with just watching them grow and not having all the answers.

I like that you saw this with your own eyes and noticed things that are hard to explain rather than just reading about it and settling for someone else's hypothesis. Thanks for sharing!