Reasonable space between defenders

[wyo96]

This situation lead to a “T” on the Team A coach, so it got me to thinking….
I see this scenario a lot and have seen all three results, PC foul, Block foul, and NO call.

4-7-2c; 10-6-7, and 10.6.7 all put the "greater responsibility for contact" on the dribbler if two defenders are less than 3 feet apart. Same applies to a defender and the boundary line.

B1 and B2 are in the lane with legal guarding position, @ 3 feet or closer apart.
A1 tries to dribble between B1/B2. As A1 moves between, B1 leans or moves his hip/knee closer to B2. (sticks out his knee may be a better description)

A1 crashes to the floor because of contact.

I tend to have no call, as I view A1 is "responsible" for the contact and the result, but I recognize that B1 did not maintain his legal position. However, I do not see a requirement that B1 and B2 must even have established legal position, only that they are less than 3 feet apart. 4-7-1a & b, require legal guarding to be established, 4-7-1c does not.

What say you?? How do you view/call this situation? Is there a reference interpretation I may be missing?