To my understanding, pressure advance only compensates for non-linearities in the extrusion process. These non-linearities, if not taken into account would thin out the path at the beginning (missing pressure) and lead to an excess of material at the end (excess pressure buildup).

With perfect compensation of these non-linearities but no changes to the target line-width and path, the minimum achievable outer radius is equal to that of the extrusion width. I’m wondering if that minimum radius could not be reduced by progressively reducing the target extrusion width the closer you get to the corner. On top of that you would need to adjust the path towards the outside in order to keep the outer wall straight.

Edit: to my understanding, a classical corner will also result in a buildup of material inside, this can be explained by the nozzle orifice dwelling longer on the inside of the corner. This excess moves to the inside, creating a round corner on the inside as well.

My proposal would also combat this inner excess, thus giving overall sharper corners.