The math we went through to come up with $25 for a month (this is where having that historical data would have been a big help) – if we knew how many visiting pilots were out-of-towners (perhaps coming into town to fly for a long weekend) and how many are SoCal locals who might come up once a month, we could make a better guess on who this would impact the most. $25 for a month means that out-of-towners (or students) would end up saving a little money (as long as they fly for 3 days or more); SoCal pilots who might just pop in for a day here and there would be paying a bit more. $20 seemed too low (you could fly for 4 months and the club would lose out) and $30 seemed a bit high (didn’t want to scare off SoCal locals).
Tried to “shoot for the middle” as much as possible to minimize impact for everyone and still maintain revenues for the club. Having all of the other multiples of months just seemed unnecessary/impractical and probably targeted at fringe cases of what people might want.