What this tells me is that you CPU miner's would find more shares if you tried to raise you ask rate from 1 to 20 or more seconds.
This is simply not true.
Your chances of finding a suitable H==0 hash are the same, regardless of whether your ask rate is 1 work unit per nonce (a few nanoseconds), or 1 work unit per 0xffffffff nonces (minutes, on a CPU).
Furthermore, the chances of working on stale work
increase as you slow down the ask rate. A 60-second period means a lot of CPU miners could waste 59 seconds worth of electricity and CPU cycles, only to discover their solution is stale and invalid.