What is the optimal size for a small group? 

It is preferable for a small group to have no more than twelve people. Five or six is the best, seven or eight is fine, and even eight or ten is good. Because we love Him and mean business with Him, we should daily pray, read the Word, learn the truth, see the light, experience Christ, and labor on Christ. Then when we come together, we will have experiences to share, rather than being an “audience” waiting for others to speak.

(On Home Meetings, chapter 1)