I too agree with Brian in that it is more just an effect. Probably typical with some wear rather than a problem as such.
At around two hundred thousand miles as several of my cars indicate or more. It seems reasonable to expect some of my fairly good engines would display simular results if I duplicated what you did. There will of course be some wear evident amoung the various components. That is to be expected.
The engine will let you know when too much has occured at some point in the distant future. I was just speculating on perhaps the cause of your effect.