Driver scripted expression problem Hello fellow blenderers.

In my recent work I try to create procedural football stadium using array modifiers. For that to work fluently I need to set up drivers and this is the point where problems start to appear. I have no idea how to force certain part of tribunes to move along with the rest. My knowledge of mathematics is rather poor and I can't crack what expression use to make it work.

The tribunes are driven by one empty that moves only on Z and Y axis. This Empty determines the height, width and angle of tribunes along with number of seats on it. Further it goes on Y axis then more rows of seats appear, Z axis determines the angle and height. Then I added the element with handrail - obviously it had to be separate object to make it appear every level of tribunes and not every row of seats. Problems start when I slide controllers to adjust width, and angle of tribunes - the handrail element simply does not follow along. I tried for couple days different combinations of expressions and nothing seems to work properly. I am attaching blend file - my drivers probably look like mess. Any other tips about drivers I could use in this project are much appreciated. 

Cheers



video example

Blend
Why don't you just use the handrail as a Start Cap model :p