How does your prescribed SRS dose vary with cavity size for treatment of resected brain metastases?

I generally follow SRS dose for postop cavities as I do for unresected lesions. 20 Gy for < 2cm, 18 Gy for <3 cm, and 16 Gy for <4cm. For tumors greater than 3 cm I have been favoring hypofractionated RT.