Excellent research. This proves what we've all suspected for a long time, that the reason the WTS insists on congos splitting when they reach a certain number of publishers is all about control.
Many JWs like being part of a big congregation. If there are 180 publishers, attendance at meetings will exceed 130 or 140 people. It means if you show up for field service, an activity many JWs secretly loathe, at least there's a posse present... it's easier to endure if 30 or 40 others show up, too. At a night meeting, the hall isn't half empty. These kinds of numbers are encouraging because no one likes to feel they're "in it alone" and lots of people in seats implies that one is part of a growing concern, that this is the place to be. The "friends" instinctively know that the real reason the congo exists is for social activity. The Society is at odds with this view; one CO told our body of elders "the congregation exists to further the preaching work. This is not a social club."
But any congregation that hits a high water mark of 160 publishers immediately feels pressure from the CO to start planning a split. Some bodies of elders, recognizing their constituents are happier in a crowd, resist the pressure. Others are all too happy to oblige because it means more important positions are created and more guys get to be presiding overseer, Watchtower conductor, and so forth. There are only five "executive" positions per congregation, so a split automatically doubles an elder's chances of getting one of those coveted posts. Watch any congregation go through a split into two, and you'll see the leading and loudest proponents are those elders who covet a position all their own. They will be fully supported by other elders who understand the control issue behind holding down the number of people in a single congo. Of course, their public stance is that they are merely supporting the society's direction and that "mother" knows best. Even reluctant elders will often go along because a split creates the (artificial) appearance of growth.
This is also the rationale behind the recent decision to increase the number of book study groups in every congregation to be sure no group numbers more than 15. Elders were told in their exclusive meeting with the CO and DO that this change would make it easier for overseers to keep a close eye on the sheep and quickly head them off if they began to stray. See, it's all about control.