ZPL and ZL1 have 3 teams
ZL2 and ZL3 have 2 teams.
Maybe just have 1 team division that acts as a 2nd Division "open" league. It would allow clubs to hold onto these mid 20 year olds who want to stay at their lifelong club and not play ZL for someone else, it also would accomodate juniors as well who miss the cut in the 20s and 18s teams.