yes its true. We had the jajenes at Tenacatita. and just as we wanted to stroll over the few feet to the other side of the ithmus, to see the sunset, they would be lurking, unseen, awaiting their evening meal! It seemed there was never enough time to stop, plaster on something to elicit most if not all those noseeums to shake their heads enough to move on. Two weeks later one could be driving to town and the itch would return, with a vengeance.
But the thing to realize is they only fly about looking for you, for a short time in the evening. So no need to get coated the entire day. Or, just miss that sunset. I used to watch the coffee percolate in the dark every winter morning, and can never remember a bite at that time. And in the heat of the day they also spent their time in their little hidy holes, to everyone's advantage.