Let's make this shader a little more flexible, and put a parameter node in it to control the IOR.

In matmatic, you use the PM function to make a parameter. Pass the initial value, and a label. It will make a math node for you and put it on the left side of the shader tree. All the non-parameter nodes will go on the right, and can be ignored when using the shader.

So this is a two line change. You want to say:

ior = PM(1.5, "IOR")
fresnel = TrueFresnel(ior)
reflect = Reflect()
combination = fresnel * reflect
surface = View(combination)

Once you make that, you can load it and then you can change the IOR on the fly without using matmatic any more.

This version, with an ior parameter, has a lot more nodes, but they are really cheap so don't worry about performance.

Attached is a render with ior = 1.2. Notice how the shallow angled edge reflections are still very bright, but the perpendicular reflections are weaker.

This is how IOR affects the reflection falloff. It doesn't change the shallowest reflections - they are still near 100%. It changes the perpendicular reflections the most.

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