is the detrmenation in group stage goal differential or home/aways goal totals?

... looking at the bracket, I like the draw, since it seems that Arsenal would feel like a away draw to Marsielle (really the only team in the bracket they have to worry about) would be a win for them, and Marsielle to be all out defensive to avoid giving Arsenal as many aways goals as possible... the other 2 teams are a decent amount of pace behind, and both arsenal and marsielle would seem to love any result that isnt a loss.

I get where Ringo is coming from w that, but I always agree with a Asenal win/draw being atleast better than 5o/5o odds... and getting over 3 to 1 on a Arsenal win, is really good value