Been wearing US4MEN and Dubio micro thongs over the years. Besides getting a nice tan on my butt side, they also expose to the sun some 70% of the sides of my ball sacks, but still hold in by the bottom enough of the balls from dangling entirely out of the swimwear. Once the testicles sides are nice and tan they blend right in. Kind of like my wife's tops expose roughly 70% of her breast cleavage, except for the areola areas.
https://www.dubiobikinis.com/Eclipse...-String-Bikini