What happens when a face is rendered  9/10x its normal size?

The minor details become integral and significant aspects of the painting, and hence, play a huge role in the interpretation and conveyance of messages.

How can different techniques —by the same author, examining the same subject— make you see it differently?

Example : Picasso’s self-portrait from ages 25-90

It allows the same object to be put through different lenses. This means the artist is revealing new, possibly contrasting perspectives of the same thing. Picasso’s portraits are an example of how his changing artistic style revealed aspects of his own perspective about himself

Can outside knowledge of an artist transform the way you see their work? Should it? 

In most cases, knowing about the artist’s background can aid in understanding the original purpose and aim the artist had in creating that piece of artwork. Sometimes, when details about the artist’s life are irrelevant to the artwork, it might blur the original meaning or value of the artwork. In these cases, whether or not the outside information should transform the way artwork is interpreted depends on the type information being used to transform your interpretation. If the details are irrelevant and insignificant, it shouldn’t deter the original view of the work.