Types of analysis like this though don't prove themselves to be predictive. These are descriptive markers, that don't really mean anything other than what happened in the past.
Trying to drill down the reason why his numbers are better hitting 3rd makes more sense, but that's like trying to ascertain why his wRC+ in May is lower than April... there's no real rhyme or reason to it, most likely.
Simply, Vlad has spent the majority of his career hitting 3rd, so... it stands to reason since he is an above average hitter overall that his best results have come hitting 3rd.