The close proximity is only cause for a foul if there is contact. You can't have a personal foul without contact.

For example, (you see this alot in girls games) A2 trys to set a screen on A1's defender B1. B1 doesn't make contact and A2 continues to move to be in B1's way. There is no foul here because there was never any contact made. If B1 would initiate contact as A2 is moving there would most likely be a foul on A2.

Hope this helps.