The pilot of the tailwheel-equipped turbine powered airplane reported that while landing, he reduced the power and there was an increased descent rate. The pilot added power but reported that the engine rpm did not have time to accelerate. The airplane touched down about 10 feet short of the runway in tall grass, the right main landing gear sheared off during the impact, the nose of the airplane dropped and the propeller impacted the ground. The airplane rotated to the left and came to a stop in a ditch, sustaining substantial damage to both the wings and their lift struts. The pilot reported there were no preimpact mechanical failures or malfunctions with the airframe or engine that would have precluded normal operation. The pilot reported as a safety recommendation, to allow plenty of runway space in case of a sudden increase in descent rate while landing.