Per their documentation @ https://www.westhash.com/?p=faq#faqs1

"You can limit your miners to work on WestHash only if the payment is good enough. You can still leave WestHash as your primary stratum server. WestHash stratum server will only be activated if the current average payment as displayed on WestHash.com front page matches your price threshold. Otherwise miners will work normally on your backup/secondary pool."


Of course I'm sure there is some variance.