I checked into this a bit, it would be non-trivial to allow only large widgets to be dragged onto the big column and vice versa. I don't know your business requirements, but I'd try to push back on this: widgets are meant to be displayed in both the large and small columns.
Thanks Aaron for your reply but i succeded in implementing such algorithm but the only problem now facing me is how to prevent dragging & dropping between the 2 coloumns ?! Is it requires modifying the draganddrop.js file ?? please help in this point, i need to prevent dragging & dropping between small & large coloumns.
thanks again for your care.