A problem with this: the partition size is multiplied by some factor when in the placement stage, but partitions at rest are not part of the calibration.

For instance, if we have topic_a and intend to double retention, we may rebalance with --partition-size-factor 2. Partition 20 may be destined for broker 1005, even accounting for a 2x partition size increase. If broker 1005 is also holding partition 15 for topic_a, what happens if both partitions 15 and 20 were to 2x in size; would the broker be pushed out of bounds?