When the purpose of the reference is to provide supporting evidence for an assertion (as appears to be the case here), I like to place the reference directly after the verb in that assertion (in this case, after "should"). However, I publish mainly in journals that use numerical citations, and you may find that, with the author-date scheme you've ...
I think the bigger problem is with your sentence structure.
However, location controls should control for variation common across
regions, while my placebo test does not provide evidence that an
unseen trend in weight gain is responsible for my results (Mincy & De
la Cruz Toledo, 2014).
By starting the sentence with "However" a contrast is ...