Under the assumption that LME yields you 36 pts./lb./gal. on average and DME yields you 40 pts/lb/gal, if you have .6 lbs of LME you are pretty much on the ball with the numbers you gave. By my calculation .6 lbs LME would yield you 21.6 pts for which you would need .54 lbs of DME to get the equivalent pts.