Allow 24" of counter for each place setting and elbow room, so you can comfortably fit 3 stools, or try to add 4, which would only cut each seating space 3" each.

i wouldnt want to be a middle person with 24" of space, much less 21.

24" is the *minimum* space, and that's with the full recommended 15" of overhang. If you have less overhang, you'll have people sitting sideways, taking up more room. If you have adults bigger than the average 150 lb that the 24" is designed for, you'll need more than 24". In fact, in almost all situations, 24" actually feels small when you're sitting crammed in there. Designing to 30" is much more comfortable.

i made this same comment on the coffee bar story yesterday. people have too many stools at their counters, making them much less appealing, its harder to pull them out and sit even if you are the sole sitter.