There was a pretty embarrassing scene in the 1st half of the Detroit game. Jeff had KP defending Tobias Harris and Harris torched the Knicks for 23 1st half points. Obviously not the best way to utilize KP as a defender. I happen to think KP can do a better job than that if he uses proper Defensive Technique, which he didn't in the 1st half. He needs to get lower and a step closer and I think he'd have more success, but still that isn't the BEST way to use KP in terms of TEAM defense.
KP is an excellent help defender and really he has good lateral movement but great straight line quickness. So he can close in from defending even a stretch 4 and still make it into the paint to protect the basket.
Notice how KP is defending Leuer but able to still close into the paint to help Sasha deal with Harris.

When Leuer was setting the pick at the top KP was able to help shut down the drive by Jackson.


This time KP was able to move his feet well in Transition and block Jackson at the rim.

Now the big story in this is that Melo was not on the floor when this happened!!! It seems that Jeff and Rambis have to decide how they want to implement KP as a TEAM Defender and do their best to keep him from having to guard Forwards on the perimeter that will look to take him off the dribble. Not every Forward has that type of game and so it should be easier to keep KP away from that situation in the future.
Additionally it is possible to start KP and Willy together effectively if Melo is no longer on the team. I think this is the 64 Million Dollar Question. Will Melo stick with the Knicks or look to move on. If he does we can put KP and Willy on the floor with a SF like Tatum for instance and it should work.
If Melo stays then you can't start KP and Willy. You have to have LT in there.