Originally Posted by fl-mike
If the un-muffed mic is hitting its AOP, then the leather muff will drop the sensitivity back into the linear region by providing an overall attenuation.
If it is at the AOP then the speech will not be adding significantly to the overall saturated signal so you will also have issues with not enough dynamics for a good squelch break when speaking as well as poor quality speech. Of course, the leather muff reduces the overall dynamic range since the mic noise floor will not move, but we are well above that.
For those not in the know, AOP = acoustic overload point or Max SPL capability. Basically, the sound pressure level at which the microphone being driven so hard that it is outputting a non-linear (distorted) signal.
Your point above is certainly viable, if the mic is being overdriven. My guess is that the mic's in question just have poor polar response or just too much low frequency response which is allowing a lot of diffuse noise to get in. Impossible to know without evaluating them.