Depending on your power costs / cooling situation, it might make sense to have your Antminer S9s running on LPM some days (regular hashrate, 88% energy usage) and on Enhanced LPM on other days (70% hashrate, 53% energy usage). This will reduce heat output and cooling costs when necessary.
If you only have a few miners, you can simply uncheck the "Enhanced Low Power Mode" checkbox in the configuration page when needed.
If you have a lot of miners, you can actually automate this process through SSH. All you have to do is add this line into the config:
"bitmain-close-low-vol-freq" : true,
There are many tools that allow you to remotely execute commands over SSH. I found the sshpass utility to be the easiest, but you could probably use pssh or ansible as well.
What do you all think?