Thanks for the advice!
What you say about training volume really makes sense. The last time I trained the lever, I did just as you described-- worked up to high volume on the adv. tuck, switched over to 1-leg lever completely when I was able to, and then saw my progress sputter and nosedive.
Based on what you've said, I'll include more variety in my lever training, with adv. tuck negatives, 1-leg negatives, and 1-leg holds as soon as I can pull them off.