InverseTransformPoint() help

I am making a script for the HTC VIVE. In my script, i am trying to find the distance between two points on an objects local axis and use this value to set the position of another object. I am attempting to achieve this using the InverseTransformPoint() function to get the distance. The current setup is as follows

I have an object(we will call object1) and childed on that object are point a and point b. Point a is static,and is the point from which I am measuring the distance. point b is what I am trying to set based off of the distance measured. I am using the vive controller as the last point(point c) and it is the second point in the distance calculation

so in theory what I want to have happen is, on a local scale i want the distance between point c (not a child of object1) and point a (is a child) to be measured; then using that measurement I want point b to be set that distance away from point a. thus setting it where the controller is but in the local space of object1.

the issue I am running into is that the point b is getting set 3.47 times further than it should which I think is due to the distance being calculated on the wrong scale. as a temporary fix I just divided by 3.47, but I'm trying to make the system reusable, and having to manually calculate this offset every time would be tedious. The code I am using is as follows:

 //calculating the distance between c and a
 controllerDistance = (object1.InverseTransformPoint(pointa.position).z - object1.InverseTransformPoint(pointc.position).z);

later in the code

 //offset should = the direction and magnitude point b needs to move
 offset = Quaternion.AngleAxis(pointa.transform.rotation.y, pointa.transform.up) * pointa.transform.forward * (controllerDistance);
 pointb.position = pointa.transform.position + offset;

please help me out I've been stuck on this for days now