I would download an app for a phone that measures frequency response- it's called RTA (Real Time Analyzer) and several free ones are available in app stores. You can go into the speaker setup menu of your AVR and when it checks the level, it sends pink noise through the speakers. As it goes from the first front speaker, it should change to the center channel- watch the response for flatness and smoothness, comparing the three front for their response. If the variations are extreme, you may see that the center channel has some frequencies that are well below the bass and midbass. If that's the case, you can manually adjust them so the sound is the way you want. If you can take photos or screen shots of the response for each speakers, post them so we can see what's happening.
If you have a laptop computer, you can download RoomEQ Wizard, but it takes a bit of time to learn- the phone app has a pretty quick learning curve.