Traditional centers as major low-post scoring threats might not be as prevalent nowadays, but they haven’t exactly gone the way of the passenger pigeon. The Pistons get to face two of them on consecutive nights — the first came Friday night when the Charlotte Bobcats and Al Jefferson visited the Palace. Tonight brings the Houston Rockets and arguably the best big man in the game in Dwight Howard. There are others but you probably don’t need more than two hands to count them. So it makes for an interesting two nights for Pistons center Andre Drummond, who will turn 21 next year. Drummond is putting up good numbers, but he definitely needs to improve his post defense. “He’s got to learn how to guard those guys on the block a little bit better, use his weight, ride them off the post a little more,” Pistons coach Maurice Cheeks said. “Just be a little more attuned in how he’s guarding a guy. He’s still learning that position in guarding that position.