KE-RATIO * (Some Decimal number per "years" of service
When I first introduced it, now nearly 7 months back, people said KE =1 is ideal. Meaning you currently hold the same amount of rewards you were given. However, after a lot of thought both slobberchops and I decided on 3.0 cut off. That gives a lot of leeway. Means it is okay to take out 3X of what you are given.
I hope a 3X factor might satisfy the years of service you are mentioning.