By "effective length," ultraman is referring to the effective top-tube length, e.g. the center-to-center distance between the head tube and the seat tube measured level with the ground from the headtube. You probably want that measure to be around 52-54cm. As frame size increases, the two "fixed" measures that increase are 1) the headtube length, and 2) the effective top tube length. The other dimensions can be adjusted away using different length stems, seaposts, crankarms, etc.