Support Interface Calibration Tower

For breakaway/dissimilar support interface materials, you should use 2 layers of 100% support interface density (no fan). Have 0 height space between the interface and the supported layer. 

For same material support interface, you should use 2 layers of 30% support interface density with 100% fan. Have one layer height of spacing between the interface and the supported layer. 

In both cases, the support interface should easily detach after the print cools down and leave a smooth top and bottom surface as if you had printed the overhang section on the buildplate.