Blended Physical material

Hello I’m having a big problem. To simplify let’s say I wan’t to make 3 footstep sounds. One is Dirt, other is Mud, and a blended one wich is Mud&Dirt (wich sounds a little bit like wet dirt). The problem is that the only thing I can get is the surface type of the physical material, wich only returns me one or another… I can’t get a blended value…
I need you guys to help me!!

(cool visualization of the problem)

Can you post the setup of the material?