OMG, mags. You clearly don't understand how to interpret stats...or even how to think about them. All you see is a number and believe that it must be saying whatever it's attempting to say. You should really try to think about what's at work when you're using stats, rather than believing in them so wholeheartedly.
So, according to this new stat teams shoot 43.9% from close range when LMA is within 5' of the hoop. That's good for 5th in the NBA. That's pretty good! But this doesn't tell you as much as you think it does. It certainly doesn't mean that LMA is the 5th best post defender in the NBA. Why not? Well, for one, LMA is RARELY within 5' of the hoop when a shot is taken from close range - he ranks #37 on the list in this regard. A great post defender would be IN THE POST PROTECTING THE HOOP a lot more than LMA is. Also, given that LMA rarely leaves his man a certain % of the 221 "shots faced" - probably a majority, though we don't have the data - are being taken by the guy he's guarding. Given that LMA is given the easiest defensive assignment, he's generally guarding bigs with lower FG%s and lesser skills - they probably shoot better than 43.9%, but again we don't have the data. Hoopdata breaks it down by "at rim" and "3'-9'", which doesn't really capture "within 5'" - perhaps averaging out the two HD percentages, and then compiling the numbers for LMA's defensive assignments would give us a better idea of just how well he's doing? I have no doubt that he's holding his opponent to a respectable FG% around the hoop. But this new stat doesn't make a case for LMA being the 5th best post defender, he just ranks 5th in OppFG% when he's within 5' of the hoop - that's it.
Looking at Appendix 2b we see that LMA is ranked #19 is Proximal FG% - that is, the FG% of shots taken when LMA is within 5' of the shot. Even this doesn't say as much as you think it might. Just by looking at the other names/ranks on the list we ought to see that there's more at play and the stat is misleading. Do you really think that LMA is a better defender than KG, Collison, Chandler, Dalembert, Noah, Asik, Gortat, etc? Is Bargnani the 2nd best defender in the league?
Just because this stat came out of MIT doesn't mean that it measures what they're trying to measure. You've got a brain, I encourage you to use it. Stats are a whole lot more than just a number - there's a whole lot of noise in them and you have to ask yourself what's being measured, what's not being measured, and what peripheral actions are affecting the measurement.