Wired Tiger Compression

Hi,

We recently upgraded out MongoDB from community version 3.4.14 to 4.0.1

We see that the compression ratio differs for the same type of data between the version

Hence we did a test and found that compression ratio drastically fell for 3.6+ 

Can you please suggest if any changes has to be made in the configuration of MongoDB or WiredTiger?

Below is the wired tiger configuration we are using

wiredTiger:
collectionConfig:
blockCompressor: zlib
engineConfig:
directoryForIndexes: true
journalCompressor: none
cacheSizeGB: 40
configString: "eviction_dirty_target=60, eviction_dirty_trigger=80, eviction=(threads_min=20,threads_max=20)"

Thanks,

Tanveer