I hadn't noticed that there was any method to the contest group matching. I thought it was completely random.

Anyway, my thoughts on the tower ranking system have been that it probably ought to have been overhauled to effectively become like a longer version of the contests. Award mojo from more sources throughout the game. Tower might still be the place for the most reliable mojo earnings rate with the arena as a so-so backup, but let there be some mojo to earn from trolls, contest results, and whatever else (girls gaining affection / xp / levels?) as well. Then set a schedule like once a week or once every two weeks (or however long they want to make it) for the tower to reset, with prizes for placement in the global listing and in your country's listing.