Without tape or some mechanical means, I find that tucking is in some ways harder post HRT. Like others, there has been significant shrinkage of both testicles and penis. And like KathyLauren mentioned, the testicles are mostly up in the body. Which is good in most ways, but not so good for that monthly tumor check we are supposed to do at some age. (Even in bed in the morning or in the shower, it takes some unpleasant contortions to wiggle those things back into manipulation range.) But the tucking is tougher because the penis is so small. For me, tight control panties don't keep it down between the legs the way they used to. It seems there just isn't enough penile material to keep all in place.
I use light urinary panty liners to flatten everything out, and that seems to do well with yoga pants and tight jeans. This would not have worked pre-HRT because of the larger size, but post-HRT, it does well for me...
Kate