Hi, 
I know that the first question that I am going to ask is probably answered by many but I would still like to understand it better. I have a system of lenses to couple light from one fiber to another(passive) whose files I have attached to this question.
It consists of 2 aspheric lenses. the fibers that I want to use for coupling light from and into are SMF-28e which have a NA(e^-2) =0.09 and a MFD of 0.0046mm. Since I read some previous discussions and solutions from Zemax staff I used to user extension calculator to calculate the Object space NA for setting the system aperture for a apodization of 1. which gave me the same value of 0.09. setting that as the object space NA in the System explorer, I still find a difference in the POP and FICL calculations. to investigate more, I also tried to plot the FICL calculation for some system aperture values which I have attached below where it becomes stable at around a object space NA =0.167 where also it matches the POP calculations. Why is it happening if POP used the MFD which is at e^-2 value and my system aperture which plays a role in FICL calculation is also clipping the rays at e^-2 value when it is set to 0.09. Shouldn't  those give the same values to me? Why do I have to increase the NA to 0.167?

Secondly, I wanted to tolerance the system and therefore look at the effects of source fiber tilts/decenters and receiving fiber tilts/decenters. The POP allows me to just put  the source fiber decenter using the Beam data tab. where the input beam is decentered but doesnt allow me to tilt the source fiber. Therefore I go to FICL to do that, although the fiber tilt of eg:+5° is much different from what i get at  -5°. shown in the pictures attached. Since the system is having cylindrical symmetry, why do I see a change there, could anyone explain that ? For the receiving fiber however, it shows the same values for corresponding negative value of the tilt or decenter, no matter you use FICL or POP. Also for the source fiber decenteres the efficiency values are the same for corresponding -ve values of decenters. Could someone please have a look and help me out in understanding this ? 
Thanks in advance