A question about the size of young level file in the implementation.

https://github.com/google/leveldb/blob/master/doc/impl.md

> When the log file reaches a pre-determined size (approximately 4MB by default), it is converted to a sorted table (see below) and a new log file is created for future updates.

> Level-0 compactions will read up to four 1MB files from level-0, and at worst all the level-1 files (10MB). I.e., we will read 14MB and write 14MB.

I can't get it. Why the size of young level sstable is 1MB, but not 4MB? Due to compression? I am not sure, because the implemetation did not mention it.