@Simkie told me about the homemade Swat and I am now on my second jar. The cons - it’s messy and leaves residue on your reins (if you care about that). The pros - it’s the ONLY thing that works for me on trail rides. Our bridle loop cuts through woods that are not so far from marshland, the deer flies have always been horrible and some days their numbers were so bad I had to turn around.
I’ve made two jars now and played around with the dilution. Right now, I’m using a 14oz jar of Vaseline with 4 capfuls (scientific, I know) of undiluted Repel-EX mixed in.
I also ride with a Cashel fly mask, sprayed with with flyspray. It helps a little, but the Vaseline-Fly Mix is the MVP. I use a tack cleaning sponge as the applicator - brush their forehead, then do a swipe down their topline on both sides.
Like you I didn’t see an overwhelming difference flyspraying the crap out of them before the ride. But the homemade Swat works. I also leave a stripe of it down their topline when I turn them out, and it does keep the B52s at bay. I’ve killed four of those monsters this summer.