I ran into this too. I’m not sure why the bias on the texture menu doesn’t work, but I found a solution in this video.
In your master material, on your Param2D node for the texture, you can change the “MipValueMode” setting to “MipBias” and it makes a “Bias” input appear. You can hardcode that or make it into a scalar parameter and adjust the bias per material instance.
The mipbias option disables anisotropic filtering, seems like the derivative option is what to use if you want to keep anisotropic. See answer to Mip bias on anisotropic filtering? - Rendering - Unreal Engine Forums