Interesting that you draw the limit at 4 players/hour for instruction. I do the same. What I found was that when the number was above 4 players/hr, that it turned into more of a 'hitting practice' versus 'hitting instruction'. Sure ... I've done group & team sessions to give an overall hitting program ... but when I've done instructional 10+ week hitting clinics with 6 & 8 players, I found myself more stressed with 6 & 8 players to get the instruction in that I wanted to get in. For me, sessions with 2-4 players work well in terms of getting the instruction across.
The NCAA used to limit four players to one coach in the off-seasons. I don't know what other colleges called them, but our coaches always called them "Four & One's" which is what we call them. Let's you give each player attention, get a ton of reps with proper rest, and there is a competition factor that starts coming in. The players push each other and they learn from each other.