Initial Guarding Postion

[Illini_Ref]

I understand how Initial Guarding Position is established and maintained. However, I am confused on when it HAS to be established to draw a PC foul.

Say A1 is dribbling toward the basket from the top of the key. B2 is chasing his man A2 from left to right at the free throw line. A2 runs through followed by B2. A1 dribbles into the side of B2. Even though there was no Initial Guarding Position, does not B2 have a right to that sopot on the floor if he got there first. This many times would be a no-call, but by rule isn't it a PC foul.

I am under the impression that initial guarding position is dealing with a defender jumping into the path of a dribbler. the rules seem to contradict themselves. A player is entitled to ANY spot on the floor as long as he gets there first, RIGHT???

SOMEONE PLEASE EXPLAIN!!!