If you are concerned your prop may be in danger of hitting the ground doing wheel landings just put the prop in the vertical position and raise the tail until it touches the ground........you may be surprised at how high you have to raise the tail in most small tail wheel airplanes
I am not concerned about my prop hitting the ground, I had my plane on a stand to fix the tailwheel and seen how much it would take for a prop strike especially with my tundra tyres, I suspect Shaggy Sheep may be right it could be a case of instructors fearing the student losing directional control also.