IIS 7 Compression not working for some websites

Hi,

I'm using Windows 2008 R2 server with IIS 7. I'm running around 10 websites in it. I enabled both Dynamic and Static Content Compression in applicationHost.config and for all websites. Two websites have the compression working and I get gzipped response. But the other websites doesn't have it worked.

For websites that doesn't get compressed, I could see few compressed files in IIS temporary folder. I understand these files are created by IIS in order to server the HTTP request.

I have set

frequentHitThreshold

frequentHitTimePeriod

Why is it working for few websites, but not for others? How can I get compression working for other websites.