I doubt if a bendi articulating truck of base capacity 1800 kg offers just 800 kg at fork height of 6 m. I am well conversant with bendi trucks and approximately 1100 kg is what it (truck of base capacity 1800 kg) should give at 6 m, at ofcourse 500 mm load centre. I would suggest rechecking the specs of the truck you are using at your end. Please let me know for any further clarification....