LCS works best when the top level is full. Then 90% of reads can be served from a single sstable. By contrast if the top level is only 10% full then 90% of reads will be served from two. This results in worse performance as well as confused users.
To address this, we can adjust the ideal top level size to how much data is actually in it (and set each corresponding lower level to 1/10 of the next one above).
(This is an idea from rocksdb.)