Simulate atmosphere and inferior or superior mirages using refraction?

I am simulating volumes of air to represent different atmospheric conditions, but I can’t seem to get any mirage effects even when using a very low index of refraction. Sometimes I can get a duplicated mirage like image, but it will be the same image orientation, not mirrored like an inferior mirage would be. I’m trying to simulate realistic temperature changes in the atmosphere using flat layers of different density. Ideally, I would like to be able to make a refractive volume with a gradient refractive index, instead of using surfaces. I’m wondering if there is any way to make the refraction angles more accurate to respond to very small changes in the refractive index. Right now I can only get light to change angle with a minimum .004 change from the value of 1, either direction. So a refractive index of .996 will bend light but .997 will not. Since the average refractive index of air is 1.00027, I can’t get seem to get any effects without a drastic change in refractive index, which probably wouldn’t happen in reality. Basically I just need some advice on the best way to accurately model our atmosphere in Unreal without having to simulate it with my own math.