IOS difference in using Compact Regular and Compact Any Size classes

I had made an application on ios for iphones portrait mode only. using Compact Any Size Classes .. its working perfectly on types of phones.

But XCode storyboard prefers to use compact Regular Size classes for all iphone portraight mode .

I am unable differenciate in them .. if i am using wrong size classes . Please someone explain with detail and reasons that which size classes i should use.

I had Read that storyboards using Any| Any size classes will work on all screen sizes including iphone 6 plus and ipad devices.

So why should it not Compact| any will not preferrable to all iphones in portraight. Please guide