Nginx helper, caching and sub-domains

I set up a multi-site using EE and have Nginx Helper enabled. “Enable Cache Purge” is checked, but I’m have some issues with sub-domains where I have to click the Purge Cache link in the header to see basic style sheet and image edits.

Am I perhaps missing some settings in the Helper plugin? (All I have enabled is the ‘Enable Cache Purge’ setting.)

Thanks in advance…