Obviously I don't know your team, but you had a bit of a different make up in between the two games, against Smeltz Stibric played big minutes, and against Northcote Larbi played bigger minutes, perhaps that could be some reason for the difference? Maybe game shape played a role as well?
Its hard to say though, but I do think the rebounding is probably the biggest advantage. The extra 10-15 shots you can get from a 2-3 zone can be a big difference.