I admit I mostly skimmed the responses but. It seems to me that you are giving off “exclusive” vibes.
First and last tanda - great! Nice couple out for a night of dancing and clearly not interested in any side action.
75% of all tandas - this couple are on date night and really only there to dance with each other. They dance with others on sufferance. They even go so far as making eye contact with each other when they dance with others!
It’s totally fine to only want to dance together but if you’re really interested in dancing with others you need to cut your couple tandas to about 4 max. Focus only on the person you’re dancing with (no eye contact or glances off the floor). Sit in a way that lets others know you’re dancing for example a chair or table between you. No hand holding or arms entwined! Only light conversation.
You've described me and my GF, especially the 'first-and-last' tanda, and about dancing 75% of the tandas together. This also seems to apply to most of the 'couples' in our community who dance this amount with their life partners. I will say, my GF typically has only a handful of leaders she's really interested in dancing with, for a variety of reasons, and tells me she's wants us to dance for most. I'm totally 'okay' with it, but know there are more and more follower friends and acquaintances stopping by and mentioning how they want to dance with me, or some I haven't danced with, but who I know are interested.
However, there have been a few instances where my experienced GF has sat out while I was out dancing, and recently counted 6 followers for me, with her only having 2 dances with leaders. We talked at great lengths about improving things, and we incorporated part of your suggestions.
We typically dance at least the first 2 tandas together, then evaluate 'who' either of us could dance with next, starting with the ones we know and have danced with before, then looking at others. We're even at the point of predicting 'who' those leaders are who'll want to dance with my GF on the drive over to our local studio, and it usually comes true, so those are expected. But putting a little distance/time between us has improved things a little. If I step away (e.g. restroom break), it has improved her success rate.
I have made it a point when we're both out dancing with other partners, I rarely, if ever, make eye contact with my GF. I will say she watches me, much more often than I watch her, and only notice her in-passing.
What also seems to work is doing a lot more 'socializing' with others, including those who she knows, and those she knows but hasn't seen in a while.
Nonetheless, overall it seems we're both satisfied with the amount of tandas we get to dance with others, while focusing on enjoying our time together (which also helps with the skills we're learning in our int-adv class and private lessons).