"Re-normalizing" is seen pretty often within the span of a round when you are an ASIC miner. I had no idea that was happening until it was mentioned. (again due to my ignorance of the method)
Any clue if the delay in high difficulty shares affects the score severely?
I guess re-normalization is affecting all, not just the fastest miners, but you may need some time to find a share after that or after a new block and higher the diff - longer the time and a block found during that time leaves you with lower income.
My hashrate is too low to mess with that, but i would target 10-20 sec per share on average