From a Leading Perspective, this one is as much your issue as it is the Followers! Why are you responsible for this issue ? 1.) It's your embrace. 2.) You have control. 3.) You're the one that's choosing vocabulary, not the Follower. 4.) Navigation! 5.) One of your jobs as a Lead (you have 3), is Music. Your job is to select the beat that the couple is dancing to and on. That is why you are responsible.
Let's go on the theory that you are ignorant of why placing the Follower in your armpit is not desirable. That you're doing what you're doing out of your own physiological comfort and ignorance:
Put simply, the Follower has a ton of physical work to do. You, my friend, have a different kind of work to do. While the role of the Follower is all about the physical, your role is intellectual - it's all about planning. You think, they do. Mind you if you think and do for them, there's not a whole lot for them to do except look nice and smile. Which is precisely what Tango was for many decades. That's not the case in today's Tango world, it's changing...slowly. The role of the Follower has expanded more over the last 2 decades. And as a result, they have more to do, and you have less to do. The more ? They're essentially being asked to execute a turn - the how the turn is done, but not when that turn is done (that's still your job). Still another instance is that they cross their feet automagically because you're not leading it 90% of the time. Still another is that in traveling ochos (what you call 'back ochos'), they're deciding how to ocho and how far that ocho goes, constantly. Put simply, they're doing the heavy lifting, while all you're doing is thinking about what should be done in time to the music.
Those three things (and there are more, these are just the prominent ones) are physical labor for the Follower. Specifically the 1st and the last. Why ? Because they require disassociation and applied disassociation (what you mistakeningly think of as a 'pivot') on the Follower's forward and back steps of their Molinete, and their ochos. 9 times out of 10 you'll start a turn to the Open side of the embrace (Lead left), using the Follower's backstep as the opening step either from a stop (bad idea by the way, see a future WHIC video on this topic), or from an ocho (better idea). That disassociation (from you) and applied disassociation in your follower tends to land them right in your armpit and thereby makes it difficult for them to get around you (for a variety of reasons which are not discussed here) for the remaining steps of the turn. The same is true of the ocho! In short, this stuff is work for them, and every time they move from the armpit, they're having to stretch to go further around you just to end up in the same place. What makes that even more challenging is that you compress the embrace, you turn away from them in turns and in crosses you place them in your armpit deliberately, and you move the center of the circle or you close the distance in crosses, and/or pull them with your left arm, your head is in the way of the turn or cross (watching their feet). Each and every time that you do this it makes their job harder and harder.