gvs, you have to throw out the average and look at what he's playing in close games. You've had a lot of blowouts, which keeps is avg minutes down. In close games, he's really playing 26-30 mins.
I'm not a fan of "tired". Experimenting is OK, but honestly, doing it for a few games is too small a sample size to give you any kind of reliable indication of effectiveness (or lack thereof).