ZKAPs are spent faster than the value of 1MB×month might imply

The lease maintenance service will renew any lease it encounters which is due to expire in 3 days or less. Since lease renewal involves setting the lease expiration time to the current time plus 31 days, this means that the practical duration of a lease may be as small as (31 days - 3 days = ) 28 days.

This is confusing. It is reasonable to summarize 31 days as "one month". It is probably even reasonable to summarize 30.5 days as "one month". 28 days is not a reasonable definition of a month.

Ultimately the renewal scheme should be replaced by a system that does not throw away part of the lease period. In the interim, we can change the lease maintenance service to let leases fully expire before renewing them. On a system with garbage collection enabled this would be somewhat dangerous but ZKAPAuthorizer is not yet in shape to do that anyway.