It seems that an extra 90 degrees needs to be added to lead-in and lead-out for rectangles. The inner cut needs to start toward the center of the innermost rectangle and instead lead in and lead out always starts on the outside of the inner rectangle.
This works great for ovals/circles but not for rectangles.
With +45deg lead-in
With -45deg lead in
The extra 90deg needs to be added or subtracted to the tangent for rectangles due to the next edge already requiring 90deg unlike circles where there is always tangency.
Thank you!