The decay system works, but it is to static since the points will only start to decay when you have reached a maximum value.
This is incorrect. The current decay system will decay points (both earned and spent) to a percentage of the original after a specified number of days, regardless of how many points someone has, even if it's 1 point.
The part of our decay that doesn't exactly work with your system is that everything decays at the same rate. If you want different things (adjustments, items, or attendances) to decay at different rates, that's not currently supported.