How to find the bisector for a line+point plane

Hello,

So I've used WB mesh offset tool in order to generate the a point for a Line+Point plane, this works fine on simple geometry but when I try offsetting more complex the shifting vertices understandably create a twist.  

I know I need to find the bisector between surfaces to get a reference point (not use wbOffset) for the LnPt plane, but I don't know how.

I've read everything I could find, but I cant understand it well enough to apply it to my definition.

My understanding to find the bisector is so far  to;

1) find the surface normals - use them as vectors

2 use the centre of the line that joins the 2 surfaces to create the origin plane needed for to calculate Angle

3) angle/2 = bisector

4?) determine the direction of offset ( I have not looked into that properly, but have seen it discussed)

I have attached the simple geometry version internalised with the wbOffset definition.

Many thanks 

James