The Suns have a lot of weaknesses purely from a personnel standpoint that limit their defensive efficiency - the really miss Amar'e's 4 boards per game - but one thing they NEED to fix from a system standpoint is in those corners. It's not a question of effort, because no matter what team we put on the floor, the two corners are blatantly and dramatically exposed in this defensive system. It was never more apparent when Richard Jefferson hit those 4 late 3-pointers in the Spurs game, and it's been killing the Suns tonight as well, but even in the games that the Suns have managed to win thus far, the Suns haven't guarded the corner at all. It's basically been a question of whether or not the opposition has been able to capitalize on the obvious weak spot by hitting the open shots that the Suns have been allowing way too often. And I don't care who it is - if you give an NBA player an open shot, he's going to knock it down more often than not.
Again, the Suns are always going to be held back by the defensive weaknesses posed by whatever lineup they field, but they can and must have a defensive system that is as air-tight as possible. Right now, they're getting killed both by what they cannot control as well as what they can.