Apply this tothe dash of a stroke in th same group as the rectangle

rectangle corrected dashes.jsx

rec = thisProperty.propertyGroup(4).content("Rectangle Path 1");
corner = rec.roundness;
x = rec.size[0];
y = rec.size[1];
myGaps = thisProperty.propertyGroup(1).gap;

diametre = Math.min(corner, Math.min(Math.max(0, x), y) / 2) * 2; // get the corrected curvature 
perimetre = (x + y - diametre * 2) * 2 + diametre * Math.PI; 

perimetre / Math.round(value) - myGaps;