well even if he has that little behind he's never putting in the rest of it with a bluff
say he plays perfectly and always folds worse on the turn and always calls better, then obviously a shove only protects us from the 10% equity villain has of winning the pot but more often gets $4 extra into the pot when we're behind

obviously villain doesn't play perfectly, but is he ever going to bluff shove river for his remaining moneys?
if so, we can call and call river and hope to pick up his leftover money
if we don't know, then shoving turn is probably best
if he's never going to bluff that little into such a large pot then go ahead and call turn, c|f river (!)