Sound/volume change

[CAO]

I have used Samsung branded LED flip covers for years, and I like the way it protects the phone. However, I have noticed on the two I have bought that if the cover is closed and the call is on speakerphone the volume is greatly reduced. However, if the cover is opened about an inch to fully opened the volume is much greater. Any suggestions on fixing this to where the volume is great even when the cover is closed. Thanks in advanced.