One thing to keep in mind in a zone is that players aren't stupid and aren't going to take well gaurded shots so just as in m2m you see your weaker defenders defend more shots, in a zone you will see weaker defenders/areas exploited. A zone will work well for you if it hides your weaknesses and your opponent is not equipped either tactically or personell wise to take advantage
one reason could be that his PG takes lot of shots against your SF, that this shots are most likely easy even if in the most sitution tronger defender is in his way and he pass the ball to other player till they find a missmatch ;)But also i am thinking how to react for the real Zone. If it wise to play 2-3 Zone against run and gun, if you know your SF lacks in OD so that your stronger guard defend those shots?