It's been known for awhile now that if a miner wishes to find more blocks than their competition - equally get more fees - they have no incentive to broadcast their blocks to more than ~30% of the hashing power. Re-deriving that number from first principles is a nice exercise in applying some basic highschool math to miner incentives. The well-known selfish mining is another example of this principle, albeit in a more advanced - active - context.