that just don't sound right to me, I can get 30+ pounds of crushed grapes in a 5 gallon pail. Granted that don't leave room for fermentation and the cap to rise but at 1.2l per pound calculates out to about a 10 gallon primary for 30lbs of grapes. This would only fill a 10 gallon primary about 1/2 full. I would think you could get a bit more in there than that.
I do not have the experience that Grapeman does with large quaintness and I am inclined to believe he knows what he is talking about however I wonder if it is not as simple as dividing 1200lbs by 1000L? I wonder if this needs to be an ascending calculation?