Thumbnail is NOT Cached on Netword Homepage

Hi..
My site using NLP 3.5.6, it is configured as WPMS-subdomain. For chaching it use W#TC with CDN activated.

On network/portal homepage (e.g. mydomain.com), display whole network posts with thumbnail. I checked the images for thumbnail is located in subdomain folder (e.g. http://subdomain1.mysite.com/wp-content/blogs.dir/5/files/2014/08/the-images.jpg)

Whole images (except NLP thumbnail) is cached and send to CDN host by W3TC function. How to make NLP thumbnail images to hosted in network (main-site) folder?
So it can be cached and send to CDN host.

I think it is very good way to reduce domain look up and gain better SEO rank. Thanks

https://wordpress.org/plugins/network-latest-posts/