6pts for every TD and 1pt for every 20 yds.
This is the same scoring system used in my league.
Ya gotta think of the numbers in context. What does it take to score 21 points using that system. Consider this -- Priest Holmes had 94 YDs rushing, 42 YDs receiving and 3 TDs and only scored 24 points.
What are the chances of Ricky duplicating that effort against an improving Philly D? I say unlikely.
Long way of saying you should be fine.