[Hummingbird Pro] Hummingbird when hosted with WPMU

I’m satisfied with the page speed on this one page site, but the score on Hummingbird isn’t ideal. My tests on Pingdom have errors that are supposedly resolved within my Hummingbird settings. So I’m wondering where the issues lie when the site is hosted with WPMU and is a small site? Why aren’t there expires headers? Why aren’t files recognized as being optimized? My goal is to get all my sites on WPMU, hoping that Hummingbird on WPMU’s own server would cache everything properly, but I’m not seeing a difference so far. Thank you for your help with this!