I would say it does but you'd have to be wearing socks as any open skin is going to get bit.
You can see it working. A fly/mosquito lands on treated surface, it just fall off dead.

You can buy Permethrin at places that carry horse/cattle products in "bulk' so to speak. You'd just have to dilute it down to percentage that is safe for humans/dogs.

I bought a 4 bottle pack which comes with ziplock bags/gloves. Each bottle treats 1 outfit, shirt/pants/socks.

I did it a little different than they recommended.
I put ALL my tripping clothes minus raingear in washing machine and added just 2 bottles. I wanted to see if getting less than what they recommended would work okay becasue I wanted to limit my exposure to the chemical.

Since it lasts thru multiple washings, I figured if it didn't work I could boost the dose before next trip.
Worked fine and now I just renew it every year with a single bottle.

I wear that ball cap/doo-rag combo and the bugs never bite my neck/ears. I think it would be the same with those ankle biter flies as long as you had socks on?

I don't go in the peak of mosquito season like you do, but I don't see them even landing on treated fabrics, just open skin.
You do your tarp they won't swarm underneath and land on it becasue it will kill them on contact.

It's cheap enough to make it at least worth a try to see if you think it's worth it?