A few years ago, I obtained a personal best in weighted chins (bodyweight plus 75lbs for 1 rep at 130lbs bodyweight) after being stuck at bodyweight plus 55lbs for a number of years. The improvement came after a couple months of Mon, Tue, Thu, Fri training on 1 arm static top holds (approximately 3-5 seconds) integrated with performing 2-3 sets of 1-3 reps of assisted one arm pull-ups.
During this period, I did no weighted chins or high rep pull-ups - just the program outlined above. In addition to the weighted chin PR, during the same time frame, I also performed an easy set of 19 pull-ups as a spur of the moment demo for some of my students.
I feel that these results were the result of focusing on the top static hold under an increased training load (i.e. the one arm hold). I did no training to increase my strength in the bottom hang position, although I wonder if working both together might have been even more beneficial.
Yours in Fitness,
Coach Sommer