With respect to comparing average bond stress with the bond strength - bond slip law, I don't get why/how these 2 should match - please explain?

Please do not forget the bond law definition in ATENA is bond slip - bond strength, not bond slip - bond stress. In other words, no elastic bond slip is being considered explicitly in the ATENA bond model (it would kind of mean double-considering the elastic deformations of the neighbouring concrete elements in the analysis), i.e., the slip is zero until the bond strength is reached.

I'm analysing the bond between ribbed reinforcement and concrete. My model consists in a steel bar (2 cm diameter) embedded in the middle of a concrete slab. In this steal bar it's applied a displacement simulating a pull-out test. I'm using the material CCReinforcementBondMaterial to model the bond law in accordance to the CEB-FIP Model Code 90.

After obtaining the results, I get the Reaction Force in the point of the steel bar where the prescribed deformation is applied, and I get the displacement in the node A (please see picture in the link below).
http://imgur.com/JSJSxxX

I'm able to determine the Average Bond Stress between the steel bar and the concrete slab using the following equation:
BondStress=ReactionForce/(L*pi*D)
where ReactionForce is the Force in the steel bar, L is the length of the connection between the steel bar and the concrete slab and D is the diameter of the steel bar.

I've analised a model with a connection length of 20 cm. Comparing the AverageBondStress/Displacement of this model with the bond law used in the material CCReinforcementBondMaterial (please see picture in the link below) we can see that these do not match.
imgur.com/JmB8nng

Also I've analised a model with a connection length of 30 cm. Comparing the AverageBondStress/Displacement of this model with the other two (please see picture in the link below) we can see that also these do not match.
imgur.com/6wCuVi8

My first question is, why aren't they coincident?

My second question is the following:
Atena 3D gives me the Bond Stress in the nodes of the steel bar. In a Step (it doesn't matter which Step it is), the bond stress in the nodes of the steel bar that are inside the concrete slab and that are nearest to node A (including node A) tend to zero (please see picture in the link below). In this nodes the bond stress should be maximum and not minimum. Why does this happens?
imgur.com/dkZSvEp

Thanks in advance.