This could just be my misunderstanding of how PoX works and what is necessary for the protocol to ensure security. We could continue that part of the discussion on the UMP 
thread as it is more peripheral to this thread. Smoothing feels like a quick fix if it is going to take longer to get to UMP.
From the perspective of a miner, in UMP, I put X amount of money in and expect to get X+Y amount in return. Additionally, the miner expects to get block decision contribution proportional to its share of the total contributions.
The UMP decides on the block and makes the transaction on the Bitcoin chain to pay the stackers. In this situation, the decision made by at least 66% of the BTC contributing parties. If one entity contributes over 66%, that one entity controls the blocks that are being added to the chain. There is no longer a chance for a smaller miner to win the block transactions decision.
unrelated butā¦ UMP could allow for a āminer bribeā attack against contracts on Stacks. As an example, letās say an auction contract on a jude NFT (laser eyes, bow tie, nyan cat background) is nearing close. An entity could buyout the UMP 66+% (as any number of miners) and prevent any other bids to the contract with roughly 2x the current miner total. Currently, with 2x the miner total, a nefarious miner could win each block with a 66% chance likelihood. 0.66 ^ N goes down pretty fast. It would take a much larger amount of BTC to ensure wining a range of blocks as it is currently.
There are always tradeoff. UMP seems to handle the current set of attacks well. Just thinking through what might be the next round.