# How to linearly blend between multiple points, deviating from a default point?

I have a set of 3D points that I need to "blend" between. Lets say I have points [A,B,C] and I have the amount I want to blend each as [0.5, 0.2, 0.8], how can I blend between these points with the amount I need? I asked this previously and got an answer.

But, when all values are 0, I need to return to a Default point, so all blending must take effect as if deviating from the Default.

How do I calculate this? I'm sure its not just a weighted barycenter anymore?

deltaA = A - Default;